Add more "Legacy RegExp" tests

[afmenez]

The 2 tests that are currently in the "esnext" tab were the existing ones moved from the "non-standard" tab, and are only a small part of the new proposal.
What is still missing:

• %RegExp% instrinsic object additional features;
• RegExpAlloc(newTarget)
• RegExpBuiltInExec(R, S)
• UpdateLegacyRegExpStaticProperties(C, S, startIndex, endIndex, capturedValues)
• InvalidateLegacyRegExpStaticProperties(C)
• RegExp.prototype.compile(pattern, flags)
• Additional properties of the RegExp constructor

As it is now, the results give the wrong impression that the specification is already implemented in Firefox, Chrome and Safari, which is not true.

[afmenez]

I believe this one deserves the "esnext" and "new test" tags. :)