For logging existing functions, currently walk the heap four times:
1) For getting the number of JS Code objects,
2) for getting the actual JS Code objects,
3) for getting the number of wasm code objects,
4) for getting the actual wasm code objects.

This CL refactors this to do only two heap walks (one for JS, one for
wasm). It also avoids the use of the brittle {ScopedVector} and uses a
{std::vector} instead.

R=thibaudm@chromium.org

Bug: chromium:1125986
Change-Id: I47e3c41ed65f4011ad8826f5e115db6459680807
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2571121
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71642}