fix(cpp): a function is named by its declarator, never by its noexcept, throw or requires clause (#2727)

Both C++ extractors name a function by the first qualified identifier
found breadth-first in its declarator, which is how an out-of-line
`Foo::bar` is named. The walk skipped only the parameter list and the
trailing return type, so a qualified name in the clauses after them
became the name of a function whose own name is plain. nlohmann/json's
constructor `basic_json(CompatibleType&& val) noexcept(noexcept(
JSONSerializer<U>::to_json(…)))` was indexed as a method
`JSONSerializer::to_json` that doesn't exist, with no node for the
constructor; `throw(std::bad_alloc)` named a method `std::bad_alloc`,
and a trailing `requires std::integral<T>` a function `std::integral<T>`.

The walk now also skips `noexcept`, `throw_specifier` and
`requires_clause`, in the TS extractor and the kernel alike; the parity
fixture covers all three.

Measured on main 226ac930 with fresh indexes, and byte-identical again
after syncing onto e97012eb: json 42, abseil 28 and
protobuf 1 phantom nodes become the real functions at the same lines;
fmt, leveldb, rocksdb, redis and three controls in other languages are
byte-identical. Kernel parity sweeps on json, fmt, abseil, leveldb and
rocksdb find no file with diffs.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/extraction/languages/c-cpp.ts

@@ -100,9 +100,11 @@ function findDeclaratorQualifiedId(declarator: SyntaxNode): SyntaxNode | undefin
     if (current.type === 'qualified_identifier') return current;
     for (let i = 0; i < current.namedChildCount; i++) {
       const child = current.namedChild(i);
-      // Don't descend into parameters or the trailing return type — their types
-      // (`const std::string&`, `-> std::string`) aren't the function name.
-      if (child && child.type !== 'parameter_list' && child.type !== 'trailing_return_type') {
+      // Don't descend into parameters, the trailing return type or the
+      // clauses after them — `const std::string&`, `-> std::string`,
+      // nlohmann/json's `noexcept(noexcept(JSONSerializer<U>::to_json(…)))`,
+      // `throw(std::bad_alloc)`, `requires std::integral<T>` name no function.
+      if (child && !DECLARATOR_NON_NAME_PARTS.has(child.type)) {
         queue.push(child);
       }
     }
@@ -110,6 +112,11 @@ function findDeclaratorQualifiedId(declarator: SyntaxNode): SyntaxNode | undefin
   return undefined;
 }
 
+/** The parts of a function declarator that hold types or expressions, never its name. */
+const DECLARATOR_NON_NAME_PARTS: ReadonlySet<string> = new Set([
+  'parameter_list', 'trailing_return_type', 'noexcept', 'throw_specifier', 'requires_clause',
+]);
+
 /**
  * Single-argument macros are ambiguous without their definition (#1373).
  * Require a preceding local #define whose replacement uses its sole parameter