This introduces an AssemblerBufferCache class which will (later) cache
the backing store of AssemblerBuffers. This is needed for PKU-protected
assembler buffers, which are expensive to allocate and deallocate.

For now, the AssemblerBufferCache does not do any caching, this will be
added in a follow-up CL.

R=thibaudm@chromium.org

Bug: v8:12809
Change-Id: I4a7ccff49c9930584a9fcda8899cfe38cfc61419
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3593136Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80145}