Detect use of "sticky" RegExp flag

[anandthakker]

IE 11 does not support the "sticky" flag for regular expressions, but eslint-plugin-compat does not seem to detect its use either as /.../y or RegExp('...', 'y')

This would be an especially helpful one to catch, since AFAIK there isn't a readily available polyfill for it. In particular, core-js, which is what Babel uses for polyfills, doesn't support it: zloirock/core-js#372.

Looks like ast-metadata-inferer specifically excludes RegExp entries: https://github.com/amilajack/ast-metadata-inferer/blob/aa3032e68afd950aecfd35590fe6d8618115df01/src/providers/index.js#L28

[brettz9]

I think this should be closed in favor of the more generic #206 (letting that apply to all ES features).