Refactor text fragment anchor state machine

This is a followup to changes started in:
https://crrev.com/c/3633947
https://crrev.com/c/3634087

This CL changes the state machine to ensure attachment happens only
twice, once on the initial InvokeSelector call and once again on the
first call after IsLoadCompleted. It also separates out keeping the
matched text scrolled in view from attachment and applying effects.

Change-Id: I98451b6f01dfaf83cba1b85f3c8e55bd7a4e1c69
Bug: 1303887
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3646700
Reviewed-by: Jeffrey Cohen <jeffreycohen@chromium.org>
Commit-Queue: David Bokan <bokan@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1011045}