Prepare for Fluid Framework upcoming deprecations

[huntj88]

Summary

Update Live Share SDK for upcoming Fluid Framework 2.90, expand compatibility coverage, and add tooling/linting to enforce internal package usage.

Key Changes

• Add compatibility check tooling and test utilities updates.
• Switch imports away from fluid-framework to @fluidframework/* and from /legacy to /internal packages where needed.
• Update Live Share core, React hooks, media, and canvas components for the new compatibility surface.
• Adjust schema/registry helpers and related tests for 2.90 changes.

[Copilot]

Pull request overview

This PR prepares the Live Share SDK for upcoming Fluid Framework 2.90 deprecations by migrating from legacy fluid-framework imports to granular @fluidframework/* packages and establishing compatibility testing infrastructure.

Changes:

• Migrated all package and sample imports from fluid-framework and fluid-framework/legacy to specific @fluidframework/* packages with /internal paths
• Added ESLint rules to enforce the new import pattern and prevent regression to deprecated imports
• Introduced compatibility testing tooling to validate builds against multiple Fluid Framework versions (2.40-2.80)

Reviewed changes

Copilot reviewed 61 out of 62 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
.eslintrc	Added no-restricted-imports rule to prevent fluid-framework imports in packages
internal/build-tools/compat-fluid.js	New compatibility testing script for multiple Fluid Framework versions
package.json	Added compat:fluid script, overrides for Fluid packages, and jest dependency
internal/usage-test/pnpm-test/package.json	Added TypeScript devDependency for build script
packages/live-share/src/**/*.ts	Updated imports from fluid-framework to @fluidframework/* packages
packages/live-share-react/src/**/*.ts	Updated imports to use @fluidframework/* and type-only imports
packages/live-share-media/src/**/*.ts	Updated imports and minor formatting improvements
packages/live-share-canvas/src/**/*.ts	Updated imports from fluid-framework to @fluidframework/tree/internal
internal/test-utils/src/**/*.ts	Updated test utility imports to use /internal paths
samples/typescript/**/*.ts	Updated sample imports to use @fluidframework/map/internal and fluid-static
samples/javascript/**/*.js	Updated sample imports and added error handling improvements
samples/javascript/21.react-media-template/src/live-share-hooks/useSharedObjects.js	Fixed URL construction bug and added localStorage error handling
samples/javascript/21.react-media-template/src/components/LiveSharePage.jsx	Added conditional background color based on Teams context
samples/javascript/02.react-video/package.json	Added jest dependency for testing

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