ES2015 Annex B.1.4 specifies a restricted pattern language for unicode
mode. This change reflects that, based on some test262 test cases.

R=littledan@chromium.org
BUG=v8:2952
LOG=N

Committed: https://crrev.com/e918c4ec464456a374098049ca22eac2107f6223
Cr-Commit-Position: refs/heads/master@{#33584}

Review URL: https://codereview.chromium.org/1645573002

Cr-Commit-Position: refs/heads/master@{#33603}