This is a reland of 10ea3f8a

Original change's description:
> [Compiler] Introduce IsCompiledScope which prevents flushing of compiled code
>
> Introduces a IsCompiledScope object which can be used to check whether a
> function is compiled, and ensure it remains compiled for the lifetime
> of the scope without being uncompiled by bytecode flushing. The Compile
> functions are modified to take a scope so that calling code can ensure
> the function remains compiled for the lifetime they require.
>
> Also, don't allocate a feedback vector for asm-wasm code as this
> is never used, and will be reallocated if the asm-wasm code fails to
> instantiate the module and we fallback to regular JavaScript.
>
> Also restructure Compiler::PostInstantiation() to allocate the feedback
> vector once, and do the optimized code check before optimizing for
> always opt.
>
> BUG=v8:8395
>
> Change-Id: I3f1a71143fcae3d1a0c01eefe91ebb4b8594221a
> Reviewed-on: https://chromium-review.googlesource.com/c/1352295
> Reviewed-by: Jakob Gruber <jgruber@chromium.org>
> Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
> Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#57971}

TBR=jgruber@chromium.org,mstarzinger@chromium.org

Bug: v8:8395
Change-Id: I8dc00798a5680997990c879c3380fe4febd47297
Reviewed-on: https://chromium-review.googlesource.com/c/1357045
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57982}