The m (multiline) and s (dotall) flags just needed to be marked as
allowed; the required logic was already in the regexp parser.

A regexp /<x>/ without the y (sticky) flag is equivalent to the sticky
regexp /.*?<x>/y.  The interpreter now assumes that every regexp is
sticky, and the compiler appends a preamble corresponding to /.*?/
before non-sticky regexps.  To reuse existing code for compiling this
preamble, the logic for each kind of quantifier is now in a separate
function and called from VisitQuantifier and for the preamble.

The commit also includes some improvements/fixes for character ranges:
- Empty character ranges/disjunctions should never match, but before
  this commit they would *always* match.
- The check of the range bounds in CanBeHandledVisitor was unncessary;
  without the unicode flag this can't be a range that can't be specified
  in 2-byte codepoints, and once we support unicode we simply support
  all codepoints.
- The capacity of the list containing the complementary intervals of a
  character range is now calculated more accurately.

Cq-Include-Trybots: luci.v8.try:v8_linux64_fyi_rel_ng
Bug: v8:10765
Change-Id: I71a0e07279b4e1140c0ed1651b3714200c801de9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2404766
Commit-Queue: Martin Bidlingmaier <mbid@google.com>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70082}