LSP: discover closed reverse importers

[nickna]

Summary

• load every root from the nearest tsconfig with the configured module, JSX, strictness, library, and ambient-type settings
• build explicit reverse dependency edges so references include closed importers without merging unrelated script globals
• expose a completeness boundary that is false for broken roots/configs and open-document-only fallback
• cover closed importers, path aliases, excludes, and complete/incomplete scopes

Verification

• dotnet test SharpTS.Tests/SharpTS.Tests.csproj --filter FullyQualifiedNameLanguageServer|FullyQualifiedNameTsConfigLoaderTests --no-restore (131 passed)
• dotnet test SharpTS.Tests/SharpTS.Tests.csproj --no-restore (16,239 passed)
• git diff --check

Refs #1306