This unifies the order of i-cache flushing and permission changing
throughout V8. According to cctest/test-icache flushing after the
permission change is not robust on some ARM32 and ARM64 devices.

There have been observed failures of {TestFlushICacheOfExecutable} on
some devices. So far there haven't been any observed failures of the
corresponding {TestFlushICacheOfWritable} test.

Also the order of flushing before the permission change is the natural
order in which the GC currently performs operations. Until we see
concrete data substantiating the opposite, the following is the
supported and intended order throughout V8:

  exec -> perm(RW) -> patch -> flush -> perm(RX) -> exec

This CL tries to establish said order throughout the codebase.

R=ulan@chromium.org
TEST=cctest/test-icache
BUG=v8:8507,chromium:845877

Change-Id: Ic945082e643aa2d142d222a7913a99816aff4644
Reviewed-on: https://chromium-review.googlesource.com/c/1351025Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57869}