feat: Add support for import attributes

[mskelton]

Re-opening #238 given the new import attributes spec is at stage 3.

tc39/ecma262#3057

Checklist:

• All tests pass in CI.
• The script/parse-examples passes without issues.
• There are sufficient tests for the new fix/feature.
• Grammar rules have not been renamed unless absolutely necessary.
• The conflicts section hasn't grown too much.
• The parser size hasn't grown too much (check the value of STATE_COUNT in src/parser.c).

[amaanq]

Hi @mskelton, I cherry picked your changes onto #291, thank you!