Run test262 tests in CI

Run test262 tests for Linux, macOS and Cosmopolitan

Add a Makefile `test2-bootstrap` helper to clone and patch test262 tests at
a particular commit. Running with the latest commit noticed a few tests were
failing and added them to the errors list.

The CI environment, especially for macOS, was a bit more unpredictable and was
failing in atomics tests due to lower timeouts in the `atomicsHelper` so double
the timeouts. The time didn't worsen too much. It still takes about 2-3 min.

test262.conf

@@ -116,6 +116,7 @@ for-of
 generators
 globalThis
 hashbang
+immutable-arraybuffer=skip
 import-attributes
 import-defer=skip
 import.meta