[P2] Evaluate Microsoft XLNT/BP parser infrastructure for X++ AST coverage

[jackyclever]

CLI/Core investigation

Determine whether Microsoft's X++ parser/AST and metadata infrastructure should replace or validate current line/regex heuristics.

Migrated from Aether #13.

Reference: Microsoft Learn — author best practice rules.

Acceptance criteria

• Build a read-only spike against representative golden X++ methods.
• Record required assemblies, licenses, platform versions, runtime/Visual Studio dependencies, and OneBox constraints.
• Compare accuracy, diagnostics, performance, and deployment complexity with a custom lexer/parser.
• Test source spans, attributes, parameters/defaults, modifiers, constructors/delegates, and call references.
• Decide and document: Microsoft adapter, custom parser, or hybrid validation.
• Keep D365FO-runtime dependencies behind an explicit platform adapter rather than portable Core.