[text-autosizer] Obey kForceOffTextAutosizing in the renderer

Previously, kForceOffTextAutosizing was checked and obeyed in the
browser via prefs.text_autosizing_enabled. But text-size-adjust is also
enabled by prefs.text_autosizing_enabled. So force-disabling the text
autosizer had the unfortunate side effect of also disabling the
text-size-adjust CSS property.

This CL obeys kForceOffTextAutosizing in the text autosizer itself such
that text-size-adjust is still enabled.

We will have to eventually change text-size-adjust's mechanism to be
something other than prefs.text_autosizing_enabled.

Bug: 428742551
Change-Id: Id5229577d64dc321aa2a26495a302063c3a140ce
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6693105
Commit-Queue: David Grogan <dgrogan@chromium.org>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Reviewed-by: Rakina Zata Amni <rakina@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1481993}