fix(extraction/cpp): keep export-macro-annotated classes and their extends edge (#946)

[luoyxy]

Summary

UE-style classes annotated with an ALL-CAPS *_API export macro
(class MYMODULE_API Name : public Base { ... }) are dropped entirely today.
tree-sitter has no preprocessor, so it reads class MYMODULE_API as an
elaborated type specifier and the whole declaration as a function_definition;
isMacroMisparsedTypeDecl then drops that phantom as unrecoverable. The result:
the class node AND its extends edge are lost, so subclass / type-hierarchy /
inheritance-impact queries return nothing for effectively every gameplay class
in an Unreal Engine project.

Fix

Add a preParse hook (blankCppExportMacros) to cppExtractor that blanks the
export macro with equal-length spaces before parsing — the same offset-preserving
technique blankCsharpPreprocessorDirectives uses (#237). The header then parses
as an ordinary class_specifier with a base_class_clause, so the class is
indexed and the existing base-clause extraction emits the extends edge, with
every symbol's line/column unchanged.

Scope is deliberately tight to avoid touching valid code: ALL-CAPS (>=2 char)
macro token, only between class/struct and the type name (two identifiers in
a row — a genuine definition never has that), and only when the type name is
followed by final, a base clause (:) or the body ({). class Foo {,
template<class T>, enum class E {, and an ALL-CAPS class name with no macro
(class FOO : public Bar) are all untouched. The existing
isMacroMisparsedTypeDecl drop path is kept as a fallback for forms this doesn't
cover (function-like macros, macros with lowercase letters).

Tests

• Existing C++: class with export macro + inheritance mislabeled as kind=function in header #946 tests upgraded from "phantom function absent" to "class node +
  extends edge present" (both class and struct variants).
• Unit tests for blankCppExportMacros: offset/length preservation, final and
  body-only headers, and non-matching cases left untouched.