fix(ts-plugin): find Astro.locals references

[qybaihe]

Fixes #16078

Summary

• include tsconfig-matched .astro files in the TypeScript plugin project
• inject the installed Astro package's env.d.ts and astro-jsx.d.ts into the TS plugin host
• add focused unit and VS Code fixture coverage for Astro.locals references

Verification

• pnpm -C packages/language-tools/ts-plugin build
• pnpm -C packages/language-tools/ts-plugin exec mocha --ui tdd --require tsx "test/units/**/*.test.mts"
• pnpm -C packages/language-tools/vscode build && pnpm -C packages/language-tools/ts-plugin test

[changeset-bot]

🦋 Changeset detected

Latest commit: 6c7ed4e

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@astrojs/ts-plugin	Patch

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