This commit adds support for capture groups (as in e.g. /x(123|abc)y/)
in the experimental regexp engine.  Now every InterpreterThread owns a
register array containing (sub)match boundaries. There is a new
instruction to record the current input index in some register.

Submatches in quantifier bodies should be reported only if they occur
during the last repetition.  Thus we reset those registers before
attempting to match the body of a quantifier.  This is implemented with
another new instruction.

Because of concerns for the growing sizeof the NfaInterpreter object
(which is allocated on the stack), this commit replaces the
`SmallVector` members of the NfaInterpreter with zone-allocated arrays.
Register arrays, which for a fixed regexp are all the same size, are
allocated with a RecyclingZoneAllocator for cheap memory reclamation via
a linked list of equally-sized free blocks.

Possible optimizations for management of register array memory:
1. If there are few register per thread, then it is likely faster to
   store them inline in the InterpreterThread struct.
2. re2 implements copy-on-write:  InterpreterThreads can share the same
   register array. If a thread attempts to write to shared register
   array, the register array is cloned first.
3. The register at index 1 contains the end of the match; this is only
   written to right before an ACCEPT statement.  We could make ACCEPT
   equivalent to what's currently CAPTURE 1 followed by ACCEPT.  We
   could then save the memory for register 1 for threads that haven't
   finished yet.  This is particularly interesting if now optimization 1
   kicks in.

Cq-Include-Trybots: luci.v8.try:v8_linux64_fyi_rel_ng
Bug: v8:10765
Change-Id: I2c0503206ce331e13ac9912945bb66736d740197
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2390770
Commit-Queue: Martin Bidlingmaier <mbid@google.com>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69929}