Add configurable Db* special-cases for MA0042/MA0045

[meziantou]

MA0042 and MA0045 were still raising await-using diagnostics for common ADO.NET factory-returned types, including the SqlDataReader scenario from #1134. In most real providers, DisposeAsync falls back to synchronous disposal in base Db* implementations, so these reports were often false positives.

Summary

• Added a new analyzer option: MA0042.enable_db_special_cases (default: true).
• Updated DoNotUseBlockingCallInAsyncContextAnalyzer await-using logic to treat Db* compile-time hierarchies as effectively sealed for:
  • DbConnection
  • DbCommand
  • DbDataReader
  • DbTransaction
  • DbBatch
• With the option enabled, factory-returned Db* values are only reported when the known hierarchy already overrides DisposeAsync below the relevant Db* base type.
• Preserved SQLite special-case behavior and precedence (existing enable_sqlite_special_cases semantics remain unchanged).
• Updated rule documentation for MA0042/MA0045 to describe the new option and default behavior.
• Expanded tests to cover:
  • new default no-diagnostic behavior for Db* factory-returned values without DisposeAsync overrides,
  • diagnostics when MA0042.enable_db_special_cases = false,
  • both MA0042 and MA0045 analyzer paths.

Validation

• dotnet test tests/Meziantou.Analyzer.Test/Meziantou.Analyzer.Test.csproj --filter "FullyQualifiedName~DoNotUseBlockingCallInAsyncContextAnalyzer_AsyncContextTests|FullyQualifiedName~DoNotUseBlockingCallInAsyncContextAnalyzer_NonAsyncContextTests"
• dotnet test tests/Meziantou.Analyzer.Test/Meziantou.Analyzer.Test.csproj /p:RoslynVersion=roslyn4.2 --filter "FullyQualifiedName~DoNotUseBlockingCallInAsyncContextAnalyzer_AsyncContextTests|FullyQualifiedName~DoNotUseBlockingCallInAsyncContextAnalyzer_NonAsyncContextTests"
• dotnet run --project src/DocumentationGenerator
• dotnet build Meziantou.Analyzer.slnx