pass_id enum (src/libponyc/pass/pass.h)

Adding or reordering values renumbers every subsequent pass id and silently breaks any code matching on specific pass ids. The Pony-side mirror in tools/lib/ponylang/pony_compiler/pony_compiler/pass.pony must be kept in sync. Run the same suites as for token changes (see core-ast-token-definitions.md): make test-pony-compiler, make test-pony-lint, make test-pony-lsp, make test-pony-doc.