Pin bundled TypeScript to v6.0.3 to fix server crash with TypeScript 7

[levanlinchik]

Pin the bundled TypeScript to 6.0.3 instead of installing typescript@latest, and keep the copy next to the language server at that version unconditionally (the worktree package.json check is removed, see below).

typescript@latest on npm is 7.x since July 8. That's the native Go compiler, and its npm package no longer ships the JS API (ts.server, createLanguageService, ...), so @vue/language-server crashes at startup:
TypeError: Cannot read properties of undefined (reading 'protocol')

6.0.3 is the last JS-based release and it's what vuejs/language-tools pin themselves. Volar isn't expected to work with TS 7 until the new compiler API ships (planned for 7.1).

The "skip install when the project has its own typescript" check is removed because:

• the server resolves typescript relative to its own install dir only, so the worktree copy was never actually used
• npm install @vue/language-server pulls typescript@latest in as a peer dependency anyway, so a broken 7.x copy ends up in the extension dir even when we skip our own install

The version check runs on every server start, so existing broken installs self-heal: installed 7.0.2 != 6.0.3 triggers a reinstall.

[cla-bot]

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[levanlinchik]

@cla-bot check

[cla-bot]

The cla-bot has been summoned, and re-checked this pull request!

[MrSubidubi]

Looks good to me, thanks and thank you for the good explanation!