Introduce a ReusableUnoptimizedCompileState class, passed to ParseInfo,
which stores a couple of pointers and most importantly the Zone and
AstValueFactory of the parse. This allows the Zone and AstValueFactory
to be reused across multiple parses, rather than re-initialising
per-Parse.

With this, we can amend the LazyCompileDispatcher to initialise one
LocalIsolate, Zone and AstValueFactory per background thread loop,
rather than one per compile task, which allows us to reduce per-task
costs and re-use the AstValueFactory's string table and previous String
internalizations.

Change-Id: Ia0e29c4e31fbe29af57674ebb10916865d38b2ce
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3313106Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78289}