This CL updates the form field states in PDFiumEngine. This is done via
setting |PDFiumEngine::in_form_text_area_| and
|PDFiumEngine::editable_form_text_area_| as per the focused annotation.
Unit tests have been added to validate the scenario.
Bug: 989040
Change-Id: I27e163819f5ca5f88e6ce10df48f2e7c7a6e97dc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2086466
Reviewed-by: Lei Zhang <thestig@chromium.org>
Reviewed-by: Kevin Babbitt <kbabbitt@microsoft.com>
Commit-Queue: Ankit Kumar 🌪️ <ankk@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#765557}
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