Sometimes the parser throws away redundant parts of the AST while
parsing.  For example, the regexp /(?:(?=(f)o))?f/ is (almost)
equivalent to just /f/ because the optional block (...)? is zero-length.
The parser notices this and returns the same tree as for /f/.  However,
there is a capture inside the (...)? block (which is never recorded
because the quantifier containing it can only match zero-width, which is
considered failure), so in this case it doesn't suffice to check that
the regexp AST doesn't contain captures.

Cq-Include-Trybots: luci.v8.try:v8_linux64_fyi_rel_ng
Bug: v8:10765
Change-Id: I6145849d95b3522a397eadd2bae63d1d8e880f28
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2397896Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Martin Bidlingmaier <mbid@google.com>
Cr-Commit-Position: refs/heads/master@{#69733}