Add suppose for compiling non-eager, non-top-level inner functions in
parallel, using the compiler dispatcher. This behaviour can be enabled
with --parallel-compile-tasks-for-lazy.

There are a couple of consequences:

  * To support this we need support for off-thread ScopeInfo
    deserialization, so this adds that too.
  * The previous --parallel-compile-tasks flag is renamed to the more
    descriptive --parallel-compile-tasks-for-eager-toplevel.
  * Both parallel-compile-tasks flags are moved onto
    UnoptimizedCompileFlags so that they can be enabled/disabled on a
    per-compile basis (e.g. enabled for streaming, disabled for
    re-parsing).
  * asm.js compilations can now happen without an active Context (in
    the compiler dispatcher's idle finalization) so we can't get a
    ContextId for metric reporting; we'd need to somehow fix this if we
    wanted asm.js UKM but for now it's probably fine.
  * Took the opportunity to clean up some of the "can preparse" logic in
    the parser.

Change-Id: I20b1ec6a6bacfe268808edc8d812b92370c5840d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3281924
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Emanuel Ziegler <ecmziegler@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78183}