[POC] Pages Metadata Diff Tool

[MrRishabhJain]

The staged code introduces a new feature called "Metadata Diff" for the Power Platform VS Code extension.

What's Added?

Feature Gate (ecsFeatureGates.ts):

Adds a new feature flag EnableMetadataDiff to control the availability of the Metadata Diff feature.
Constants (Constants.ts):

Defines telemetry event names for initialization and error handling related to Metadata Diff.
Metadata Diff Initialization (MetadataDiff.ts):

Initializes the Metadata Diff feature based on the ECS feature flag.
Sets VS Code context (microsoft.powerplatform.pages.metadataDiffEnabled) to control UI visibility.
Logs telemetry events for initialization success or failure.
Tree Data Provider (MetadataDiffTreeDataProvider.ts):

Implements a VS Code Tree Data Provider to display file differences.
Recursively scans workspace files, creates backup copies, and mocks file changes for testing.
Builds a hierarchical tree structure representing changed files and folders.
Tree Items (MetadataDiffTreeItem.ts, MetadataDiffFileItem.ts, MetadataDiffFolderItem.ts):

Defines abstract and concrete classes for tree items representing files and folders.
Implements commands to open file diffs using VS Code's built-in diff viewer.
Extension Activation (extension.ts):

Registers the Metadata Diff Tree Data Provider with VS Code.
Initializes the Metadata Diff feature during extension activation.
Localization (package.nls.json, bundle.l10n.json):

Adds localized strings for the Metadata Diff feature.
Package Manifest (package.json):

Registers the new Metadata Diff view in the VS Code explorer.