Add user agent to token calls

[bbirman]

Confirmed with Charles that Android includes the MSDK user agent on the equivalent requests for accessTokenForApprovalCode and accessTokenForRefresh, updating iOS to match

[bbirman]

I think there used to be more in this protocol but I don't see it used anywhere (even for mocking) so I don't think it needs to be public, the one method was used as a helper method for SFNetwork and with this change it's not needed

[github-actions]

	1 Warning
⚠️	Static Analysis found an issue with one or more files you modified. Please fix the issue(s).

Clang Static Analysis Issues

File	Type	Category	Description	Line	Col
SFOAuthCoordinator	Nullability	Memory error	nil assigned to a pointer which is expected to have non-null value	120	19
SFOAuthCoordinator	Nullability	Memory error	nil assigned to a pointer which is expected to have non-null value	370	15
SFOAuthCoordinator	Nullability	Memory error	nil assigned to a pointer which is expected to have non-null value	380	15

Generated by 🚫 Danger

[github-actions]

	Tests	Passed ☑️	Skipped	Failed ❌️
SalesforceSDKCore iOS ^18 Test Results	587 ran	585 ✅		2 ❌

Test	Result
SalesforceSDKCore iOS ^18 Test Results
DomainDiscoveryCoordinatorTests.testCallbackSuccess()	❌ failure
SFUserAccountManagerTests.testUserAccountEncoding (failure 1/3)	❌ failure
SFUserAccountManagerTests.testUserAccountEncoding (failure 2/3)	❌ failure
SFUserAccountManagerTests.testUserAccountEncoding (failure 3/3)	❌ failure

• View SalesforceSDKCore iOS ^18 Test Results

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 63.42%. Comparing base (e8a07ac) to head (37e36a8).
⚠️ Report is 22 commits behind head on dev.

Files with missing lines	Patch %	Lines
...KCore/SalesforceSDKCore/Classes/Util/SFSDKOAuth2.m	37.50%	5 Missing ⚠️

❌ Your patch status has failed because the patch coverage (66.66%) is below the target coverage (80.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #3975      +/-   ##
==========================================
- Coverage   63.44%   63.42%   -0.02%     
==========================================
  Files         252      252              
  Lines       22137    22143       +6     
==========================================
+ Hits        14044    14045       +1     
- Misses       8093     8098       +5     

Components	Coverage Δ
Analytics	70.78% <ø> (ø)
Common	69.76% <ø> (ø)
Core	54.05% <66.66%> (-0.02%)	⬇️
SmartStore	74.59% <ø> (ø)
MobileSync	87.53% <ø> (ø)

Files with missing lines	Coverage Δ
...lesforceSDKCore/Classes/OAuth/SFOAuthCoordinator.m	42.42% <100.00%> (+0.26%)	⬆️
...SalesforceSDKCore/Classes/OAuth/SFSDKAuthSession.m	91.42% <100.00%> (+0.80%)	⬆️
...KCore/SalesforceSDKCore/Classes/Util/SFSDKOAuth2.m	55.20% <37.50%> (ø)

... and 2 files with indirect coverage changes

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[github-actions]

	Tests	Passed ☑️	Skipped	Failed ❌️
SalesforceSDKCore iOS ^26 Test Results	587 ran	586 ✅		1 ❌

Test	Result
SalesforceSDKCore iOS ^26 Test Results
DevInfoViewControllerTests.testDevInfoViewRendersRealWorldData()	❌ failure

• View SalesforceSDKCore iOS ^26 Test Results