With the recent switch from the tasks API to the jobs API for thread
management within WebAssembly compilation we got the problem that
TurboFan compilation of a previous compilation can block the Liftoff
compilation of a new compilation. With synchronous compilation, this can
cause significant delays for the user. With this CL we increase the
priority of synchronous compilation so that at least synchronous
compilation can only be blocked by other synchronous compilation. This
fixes issues that we saw on autocad.

Why is it okay to increase the priority of synchronous compilation?
* On the main thread, synchronous compilation is only allowed for small
  modules which should not take long to compile. Also, the compilation
  blocks the main thread and should finish as fast as possible.
* On worker threads, delaying other background work is not such a big
  issue.

Downsides:
* This does not only increase the priority of the initial compilation,
  but also for the TurboFan optimization. Similar to above, for small
  modules on the main thread this should not be a big deal because
  compilation is fast. Big modules can only be compiled on worker
  threads.

Note that this is supposed to be a fix for the problems we see at the
moment with autocad on stable and beta. Eventually compilation job
management should be done by the wasm engine for all WebAssembly
compilation, so that not each WebAssemly module has to do its own
compilation job management.

R=clemensb@chromium.org

Bug: chromium:1142686, v8:11088
Change-Id: Iee4948b2fcad944f587918e9452e6888258857f9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2512911
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70923}