feat(csharp): index C# 12 primary constructors via an up-to-date grammar (#237) (#717)

Vendor tree-sitter-c-sharp 0.23.5 (ABI 15) for C#, replacing the bundled ABI-13
build that dropped primary-constructor classes. Adds native primary-ctor
parsing, primary-ctor parameter dependency edges, return-type extraction via the
renamed `returns` field, and a preParse that blanks `#if` directive lines the
new grammar mis-parses inside enum bodies. Validated on MediatR / eShopOnWeb /
Newtonsoft.Json + full suite.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/extraction/tree-sitter-types.ts

@@ -78,6 +78,16 @@ export interface ExtractorContext {
  * language-specific details like signatures, visibility, and imports.
  */
 export interface LanguageExtractor {
+  /**
+   * Optional source transform applied immediately before the grammar parses the
+   * file. Used to work around grammar gaps that would otherwise corrupt the
+   * parse tree (e.g. C# blanks conditional-compilation directive lines the
+   * grammar mis-parses inside enum bodies). MUST preserve byte offsets (replace
+   * removed text with spaces, keep newlines) so node positions and getNodeText
+   * stay correct; the returned string is used for both parsing and extraction.
+   */
+  preParse?: (source: string) => string;
+
   // --- Node type mappings ---
 
   /** Node types that represent functions */