feat(extraction): index Metal shader files (.metal) via the C++ grammar (#1121) (#1151)

.metal was absent from EXTENSION_MAP, so Metal Shading Language files were
silently skipped. MSL ≈ C++14, and the C++ grammar extracts its functions,
structs, type aliases, and call edges at parity with plain C++ — except MSL's
post-declarator [[attribute]] annotations, which misparse struct fields into
spurious extends refs from the struct to the field's own type (a wrong
inheritance edge whenever the repo typedefs float3/float4x4 itself, common in
shared ShaderTypes.h). blankMetalAttributes blanks them pre-parse,
offset-preserving, following the blankCppExportMacros pattern (#1061), gated
to .metal files only — in regular C++ the attribute position is legal syntax
the grammar parses natively. The preParse hook gains an optional filePath
param to support the gate.

Validated on llama.cpp's ggml-metal.metal (10.7k lines: 130 kernels vs 113
`kernel void` ground-truth lines, rope_yarn resolves its 4 kernel callers)
and SDL's shaders (PQtoLinear ← GetOutputColor), 0 bogus extends edges.

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

src/extraction/tree-sitter-types.ts

@@ -85,8 +85,10 @@ export interface LanguageExtractor {
    * 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.
+   * `filePath` lets a transform key off the concrete file extension when one
+   * language id serves several dialects (C++ also parses `.metal` shaders).
    */
-  preParse?: (source: string) => string;
+  preParse?: (source: string, filePath?: string) => string;
 
   // --- Node type mappings ---