Add more tests for for (async of edge-cases

[Zalathar]

This adds tests for two more edge-cases related to the for (async of restriction (tc39/ecma262#2256):

for (\u0061sync of [7]);

In this case, the identifier async is written with an escape sequence. This avoids the async of lookahead, which only considers non-escaped words.

This detects implementations that check for an async token without considering whether it was escaped.

Recently fixed in V8: https://bugs.chromium.org/p/v8/issues/detail?id=11722

for ((async) of [7]);

In this case, the identifier token async is preceded by a ( token, which avoids the async of lookahead because async is no longer the first token in the head.

This detects implementations that check whether the LHS is an identifier at the AST level, without considering parentheses.

Motivated by babel/babel#13244 (review).

[jugglinmike]

Very nice. Thanks for revisiting this!

[ghost]

test/language/statements/for-of/head-lhs-async-parens.js

[jugglinmike]

Hi there, @Zalathar. Test262 requires all contributors from non-Ecma member organizations sign a Contributors License Agreement. I forgot to ask you to do that--sorry! Would you mind signing it, now? It's totally okay if you can't; we'll just have to revert your patch.

[Zalathar]

A CLA should be fine, but where can I find a privacy policy for the sensitive personal information required by the form?

[jugglinmike]

@Zalathar I can't answer your questions myself, but I'm working to find someone who can (hence the delay). I'll keep you posted.