fix: allow keywords as property names after . and \.

[otnc]

Summary

Property access resolved names through a fixed keyword allowlist, and every other keyword fell through to "unknown" — so promise.then[f] compiled to p.unknown(f). The entire Promise chaining API (then / catch / finally) and any keyword-named member was broken.

Changes

• New keyword_text helper maps every keyword token back to its source text
• New Parser::parse_property_name used in property position (after . and \.), accepting any keyword — matching JavaScript, which allows reserved words as property names

p.then[f].catch[g].finally[h]
-- before: p.unknown(f).unknown(g).unknown(h)
-- after:  p.then(f).catch(g).finally(h)

Binding positions (destructuring, parameters, import names) keep the previous stricter allowlist.

Known limitation

protected and function lex to the same tokens as private / fn, so obj.protected compiles to obj.private (pre-existing token-level aliasing; unchanged by this fix).

Tests

• moon test --target js: 322 passed
• Added parser tests (p.then[f], p.catch[f], p.finally[f], obj.if, obj\.then) and codegen tests for the full promise chain
• E2E: compiled and executed a real Promise.resolve[...].then/catch chain via pkg/index.js

Fixes #6