We set the bit_field_2 fields at map construction.

Bug: v8:7790, chromium:1150811
Change-Id: I673334d6900993b8a52e3b85d504cbc3f457c020
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2773053
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73638}