Fix SQL generated column indexing

[Widthdom]

Summary

• index SQL generated/computed columns from CREATE TABLE and ALTER TABLE ADD
• emit generated_column_dependency references for generated expressions and DEFAULT NEXT VALUE FOR sequences
• add SQL symbol/reference regression tests

Validation

• dotnet build CodeIndex.sln -c Release -p:UseSharedCompilation=false
• dotnet test CodeIndex.sln -c Release -p:UseSharedCompilation=false --filter "FullyQualifiedNameReferenceExtractorTests.Extract_SQL_|FullyQualifiedNameReferenceExtractorTests.Extract_Sql|FullyQualifiedName~SymbolExtractorTests.Extract_SqlGeneratedColumns_DetectsColumnSymbols"

Documentation / Changelog

• changelog.d/unreleased/2102.fixed.md

Follow-up candidates

• None

Fixes #2102