feat(core/core-util): migrate to #platform/* imports

[deyaaeldeen]

Migrate @azure/core-util build config to per-platform tsconfigs under config/, update eslint and vitest configs. No source changes — this package has no platform-specific code.

[Copilot]

Pull request overview

This PR migrates @azure/core-util’s build/test/lint configuration to the repo’s per-platform config/-scoped tsconfigs (for browser/react-native/esm/cjs) and updates Vitest and ESLint wiring accordingly, without changing the library source.

Changes:

• Add per-platform Warp build targets pointing at package-local config/tsconfig.src.*.json.
• Replace root-level tsconfig files with config/ equivalents and update TS project references.
• Switch browser Vitest config to the shared eng/vitestconfigs/browser.config.ts and add a flat eslint.config.mjs.

Reviewed changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
sdk/core/core-util/warp.config.yml	Overrides Warp targets to use package-local per-platform tsconfigs.
sdk/core/core-util/vitest.browser.config.ts	Re-exports the shared browser Vitest config from eng/vitestconfigs/.
sdk/core/core-util/package.json	Updates test scripts to run tsc -b --noEmit and simplifies Vitest invocation.
sdk/core/core-util/eslint.config.mjs	Adds ESLint flat config pointing at config/tsconfig.lint.json.
sdk/core/core-util/tsconfig.json	Updates project references to new config/ tsconfigs.
sdk/core/core-util/config/*	Adds per-platform src/test/snippets/lint tsconfigs used by build/test/lint.
sdk/core/core-util/review/core-util-browser.api.diff.md	Adds browser-vs-node API report diff artifact for review.
(deleted) sdk/core/core-util/tsconfig.*.json	Removes legacy root-level tsconfig files replaced by config/ versions.