It was not in sync with the optimization, which relies on
inspecting up the length and name fields even for bound
functions.

To make a now meaningful serializer test actually pass, I have
to to make some changes to the test setup.

I'm also moving the function name and length index constants
from JSFunction to JSFunctionOrBoundFunction for clarity.

TBR=marja@chromium.org

Bug: v8:7790
Change-Id: I36dd3c80996ccb53810c7ea9bfceb5c84ffd60ab
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2972919
Commit-Queue: Georg Neis <neis@chromium.org>
Reviewed-by: Santiago Aboy Solanes <solanes@chromium.org>
Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75299}