[dart2wasm] Fix ignoreCase for regexp.
[dart2wasm] Fix ignoreCase for regexp.

Change-Id: I62eef6ba1a09a3270f0bf338bdf82eb28d36b410
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/267161
Commit-Queue: Joshua Litt <9f8daed1ab51574c9a48ffacb03e4a1adb4f880c@google.com>
Reviewed-by: Aske Simon Christensen <589eb3fd9a84f06d0ac46d3aa71dddcfb0814ccd@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk