The WasmCodeManager was part of the WasmEngine so far, but there is only
exactly one WasmEngine. Hence we can pull it out, and also remove the
pointer in the WasmCodeAllocator.

The argument passed from the single constructor call is now inlined in
the constructor itself.

Drive-by: Replace "GetPlatformPageAllocator()->CommitPageSize()" by just
"CommitPageSize()".

R=jkummerow@chromium.org

Bug: v8:11879
Change-Id: I6c0e74cea308f5806d1aa479945d90b6ef8d1613
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2972909
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75270}