ClangAstParser: rename misleading version/Clang_3_8 class #262

The bundled Clang AST dumper is v18 (v18.1.8_4), yet the only class under ClangAstParser/src/pt/up/fe/specs/clang/version/ is named Clang_3_8:

// ClangStreamParserV2.java:36
addWorker(() -> new ClavaNodeParser(Clang_3_8.getClassesService()));

Its sole content is an AlignedAttr classname mapping — it is a historical leftover name, not actual multi-version support. The version/ package invites readers to hunt for version-specific paths that don't exist.

Proposal: rename it to something accurate (e.g. DumperClassMappings) and consider flattening the version/ package.