Core AST / token definitions

Changes to token definitions (token.h), AST node types, the lexer, parser, AST manipulation, sugar/desugaring passes, or subtype checking can break the tools and pony-compiler tests. Adding or reordering token enum values renumbers every subsequent token and silently breaks any code matching on specific TK_* types. Run: make test-pony-compiler, make test-pony-lint, make test-pony-lsp, make test-pony-doc.