Some of these tests pass the pattern as a string, and in this case
there's a subtle distinction between

"/\u{0041}/"  // Unicode escape interpreted in string literal.

and

"/\\u{0041}/"  // Unicode escape interpreted by regexp parser.

Extend these tests to check both cases.

Thanks littledan@ for pointing this out.

BUG=v8:5437

Review-Url: https://codereview.chromium.org/2839923002
Cr-Commit-Position: refs/heads/master@{#44840}