chore: Remove MULTICHAIN_API feature flag and expose Multichain API on all build types

[adonesky1]

Previously the Multichain API was only available on Flask and Beta builds. Starting in 12.18.0 we are releasing the Multichain API to all build types including stable

Related issues

Fixes: https://github.com/MetaMask/MetaMask-planning/issues/4779

Manual testing steps

1. Build this branch in a normal stable build (yarn start)
2. Go to https://metamask.github.io/test-dapp-multichain/latest/
3. Enter your extensionId (watch video below to see where) -> Detection on stable blocked by 22.1.0 providers#420
4. See that you're able to connect and interact with the multichain api

Screenshots/Recordings

Before

Screen.Recording.2025-04-28.at.2.44.45.PM.mov

After

Screen.Recording.2025-04-28.at.3.50.31.PM.mov

Pre-merge author checklist

• I've followed MetaMask Contributor Docs and MetaMask Extension Coding Standards.
• I've completed the PR template to the best of my ability
• I’ve included tests if applicable
• I’ve documented my code using JSDoc format if applicable
• I’ve applied the right labels on the PR (see labeling guidelines). Not required for external contributors.

Pre-merge reviewer checklist

• I've manually tested the PR (e.g. pull and build branch, run the app, test code being changed).
• I confirm that this PR addresses all acceptance criteria described in the ticket it closes and includes the necessary testing evidence such as recordings and or screenshots.

[github-actions]

CLA Signature Action: All authors have signed the CLA. You may need to manually re-run the blocking PR check if it doesn't pass in a few minutes.

[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	@​metamask/​providers@​22.0.1 ⏵ 22.1.0				+1

View full report

[metamaskbot]

Builds ready [bb269c3]

• builds: chrome, firefox
• builds (beta): chrome
• builds (flask): chrome, firefox
• builds (test): chrome, firefox
• builds (test-flask): chrome, firefox
• build viz: Build System
• bundle size: Bundle Size Stats
• user-actions-benchmark: User Actions Stats
• storybook: Storybook
• typescript migration: Dashboard
• all CircleCI artifacts
• bundle viz:

  • background: 0, 1, 2, 3, 4, 5, 6, 7, 8
  • common: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14
  • ui: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13
  • content-script: 0
  • offscreen: 0

UI Startup Metrics (1182 ± 70 ms)

Platform	BuildType	Page	Metric	Mean (ms)	Min (ms)	Max (ms)	Std Dev (ms)	P 75 (ms)	P 95 (ms)
Chrome	Browserify	Home	uiStartup	1182	1052	1470	70	1214	1320
			load	1027	924	1322	63	1052	1147
			domContentLoaded	1022	920	1307	62	1048	1141
			domInteractive	16	13	32	4	16	27
			firstPaint	682	77	1170	408	1037	1106
			backgroundConnect	6	4	18	2	7	9
			firstReactRender	20	14	44	5	20	33
			getState	13	5	36	8	19	30
			initialActions	0	0	4	0	0	1
			loadScripts	788	698	963	56	815	902
			setupStore	8	5	14	2	8	12
	Webpack	Home	uiStartup	2132	1729	2487	156	2236	2353
			load	1641	1343	2073	122	1729	1833
			domContentLoaded	1634	1339	2069	122	1723	1829
			domInteractive	16	11	61	10	13	46
			firstPaint	175	77	354	64	203	320
			backgroundConnect	24	9	80	14	28	61
			firstReactRender	195	55	391	119	333	357
			getState	14	4	295	29	13	25
			initialActions	3	1	6	1	3	5
			loadScripts	1629	1338	2067	122	1721	1815
			setupStore	25	6	297	45	23	38
Firefox	Browserify	Home	uiStartup	1318	1120	1790	119	1373	1573
			load	1177	1000	1659	120	1234	1452
			domContentLoaded	1176	1000	1659	120	1234	1452
			domInteractive	99	35	220	27	113	144
			firstPaint	NaN	NaN	NaN	NaN	NaN	NaN
			backgroundConnect	21	13	213	21	20	34
			firstReactRender	22	19	55	6	22	31
			getState	7	4	25	3	8	15
			initialActions	0	0	1	0	0	1
			loadScripts	1159	988	1636	120	1218	1438
			setupStore	6	3	32	3	6	8
	Webpack	Home	uiStartup	1494	1361	1983	123	1560	1742
			load	1283	1155	1682	104	1354	1486
			domContentLoaded	1282	1154	1681	104	1353	1486
			domInteractive	82	34	167	21	96	126
			firstPaint	NaN	NaN	NaN	NaN	NaN	NaN
			backgroundConnect	25	14	108	15	24	78
			firstReactRender	34	28	55	5	36	44
			getState	9	4	34	6	9	29
			initialActions	0	0	2	1	1	1
			loadScripts	1261	1116	1655	103	1333	1466
			setupStore	11	5	268	26	8	26

Benchmark value 78 exceeds gate value 49 for firefox webpack home p95 backgroundConnect
Sum of mean exceeds: 0ms | Sum of p95 exceeds: 29ms
Sum of all benchmark exceeds: 29ms

Bundle size diffs [🚨 Warning! Bundle size has increased!]

• background: 9.33 KiB (0.18%)
• ui: -261 Bytes (0%)
• common: 0 Bytes (0%)

[jiexi]

it's time 🚀

[metamaskbot]

Builds ready [66fd474]

• builds: chrome, firefox
• builds (beta): chrome
• builds (flask): chrome, firefox
• builds (test): chrome, firefox
• builds (test-flask): chrome, firefox
• build viz: Build System
• bundle size: Bundle Size Stats
• user-actions-benchmark: User Actions Stats
• storybook: Storybook
• typescript migration: Dashboard
• all CircleCI artifacts
• bundle viz:

  • background: 0, 1, 2, 3, 4, 5, 6, 7, 8
  • common: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14
  • ui: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13
  • content-script: 0
  • offscreen: 0

UI Startup Metrics (1187 ± 60 ms)

Platform	BuildType	Page	Metric	Mean (ms)	Min (ms)	Max (ms)	Std Dev (ms)	P 75 (ms)	P 95 (ms)
Chrome	Browserify	Home	uiStartup	1187	1072	1372	60	1225	1321
			load	1029	943	1199	53	1057	1145
			domContentLoaded	1023	909	1193	53	1053	1138
			domInteractive	17	13	59	7	16	32
			firstPaint	732	81	1199	397	1041	1092
			backgroundConnect	7	4	80	7	7	10
			firstReactRender	21	16	57	7	22	37
			getState	13	5	102	12	17	28
			initialActions	0	0	1	0	0	1
			loadScripts	788	668	967	52	816	894
			setupStore	8	5	21	3	8	15
	Webpack	Home	uiStartup	2159	1773	2570	164	2269	2405
			load	1674	1373	2049	137	1769	1915
			domContentLoaded	1668	1369	2045	135	1765	1879
			domInteractive	15	12	45	8	13	39
			firstPaint	181	64	406	69	231	319
			backgroundConnect	28	9	182	22	32	64
			firstReactRender	214	56	363	114	324	350
			getState	12	4	55	7	14	25
			initialActions	3	1	7	1	4	5
			loadScripts	1663	1368	2043	135	1764	1855
			setupStore	20	6	174	17	23	34
Firefox	Browserify	Home	uiStartup	1342	1145	1759	116	1404	1556
			load	1199	993	1584	117	1277	1418
			domContentLoaded	1199	993	1584	117	1277	1418
			domInteractive	102	41	265	35	113	168
			firstPaint	NaN	NaN	NaN	NaN	NaN	NaN
			backgroundConnect	18	13	37	4	19	29
			firstReactRender	22	19	59	5	22	27
			getState	7	4	27	3	8	10
			initialActions	0	0	2	0	0	1
			loadScripts	1183	982	1561	116	1263	1400
			setupStore	8	4	206	20	6	15
	Webpack	Home	uiStartup	1513	1328	1924	117	1595	1730
			load	1294	1145	1640	102	1380	1488
			domContentLoaded	1293	1144	1640	102	1380	1488
			domInteractive	86	33	237	28	97	129
			firstPaint	NaN	NaN	NaN	NaN	NaN	NaN
			backgroundConnect	22	15	54	7	23	36
			firstReactRender	36	29	79	6	37	45
			getState	9	4	29	5	9	26
			initialActions	1	0	2	1	1	1
			loadScripts	1274	1131	1616	101	1350	1470
			setupStore	12	5	260	26	8	30

Benchmark value 30 exceeds gate value 28 for firefox webpack home p95 setupStore
Sum of mean exceeds: 0ms | Sum of p95 exceeds: 2ms
Sum of all benchmark exceeds: 2ms

Bundle size diffs [🚨 Warning! Bundle size has increased!]

• background: 9.33 KiB (0.18%)
• ui: -261 Bytes (0%)
• common: 0 Bytes (0%)