Reland "[wasm] Remove fixed limit on number of background tasks"

This is a reland of 54379af9. Instead
of removing the limit completely, this limits to 128 parallel tasks
now. This avoids some special handling for the previous default value
of -1.

Original change's description:
> [wasm] Remove fixed limit on number of background tasks
>
> After fixing https://crbug.com/v8/8916, background compilation scales
> far beyond 10 threads, especially for TurboFan (where much more work is
> parallelizable). Thus, remove the limit of 10 background compilation
> tasks, and use all available threads instead.
>
> R=mstarzinger@chromium.org
>
> Bug: v8:8916
> Change-Id: I13c30777e3c85b2de7901b5eac3e6a41457a56f9
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1893348
> Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
> Commit-Queue: Clemens Backes <clemensb@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#64724}

Bug: v8:8916, chromium:1021442
Change-Id: Ie9a9368c74d26c4595c0e94e914b025e403daaa4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1899991Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64828}

src/flags/flag-definitions.h

@@ -644,8 +644,8 @@ DEFINE_BOOL(assume_asmjs_origin, false,
             "force wasm decoder to assume input is internal asm-wasm format")
 DEFINE_BOOL(wasm_disable_structured_cloning, false,
             "disable wasm structured cloning")
-DEFINE_INT(wasm_num_compilation_tasks, 10,
-           "number of parallel compilation tasks for wasm")
+DEFINE_INT(wasm_num_compilation_tasks, 128,
+           "maximum number of parallel compilation tasks for wasm")
 DEFINE_DEBUG_BOOL(trace_wasm_native_heap, false,
                   "trace wasm native heap events")
 DEFINE_BOOL(wasm_write_protect_code_memory, false,