Add semantic references support

[nickna]

Part of #1306.

Summary:

• add an inverse checker binding index with declaration filtering and type/value facet unioning
• expose textDocument/references only in full language-feature mode
• share one checked navigation model between definition and references
• discover the connected component across open roots so reverse importers are included without merging unrelated script globals
• preserve aliases and re-export occurrences across module boundaries
• document why safe rename still waits for a complete reverse workspace graph

Testing:

• dotnet build SharpTS.sln --no-restore
• focused definition/reference tests: 29 passed
• dotnet test SharpTS.Tests/SharpTS.Tests.csproj --no-restore: 16,234 passed