Now that Asm.js code is also context independent, move code to ensure context independence
from BytecodeGenerator to FinalizeUnoptimizedCode.

Reland of CL: https://chromium-review.googlesource.com/c/v8/v8/+/1349236

Change-Id: I718090850870c61733e0719d4091ec60bc080ebb
Reviewed-on: https://chromium-review.googlesource.com/c/1396201
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58558}