Avoid project crash for unknown file types

[Copilot]

Opening a file with an unrecognized extension/language ID could flow ScriptKindUnknown into the project parse cache. The parser rejects unknown script kinds and panicked, taking down the server.

• Root cause

  • Unknown editor language IDs (for example vue) plus unknown file extensions produced ScriptKindUnknown.
  • Inferred projects allow non-TS extensions, so the file reached parsing instead of being filtered out.

• Fix

  • Default unknown project file script kinds to TypeScript before acquiring the parse cache, matching TypeScript’s ensureScriptKind fallback behavior.

scriptKind := fh.Kind()
if scriptKind == core.ScriptKindUnknown {
    scriptKind = core.ScriptKindTS
}

• Regression coverage
  • Added a project test that opens component.vue with language ID vue and verifies the language service can load it without crashing.