Checks if a page is readable before calling Read Aloud

Checks if the URL is supported before sending a readability request.
The following URLs won't be supported:
- URL without an https or http scheme
- myactivity.google.com/...
- myaccount.google.com/...
- www.google.com/... [based on Google's domain guidelines,
www.google.com/ has been reserved for Search content and features]

The original test for invalid URLs has been expanded with more
unsupported URLs.

Bug: b/291129429
Change-Id: I6ed384b40eb2343e0d5bc791e3cc3145a52b9896
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4717392


Reviewed-by: Basia Zimirska <basiaz@google.com>
Reviewed-by: Bo Liu <boliu@chromium.org>
Code-Coverage: Findit <findit-for-me@appspot.gserviceaccount.com>
Commit-Queue: Andrea Gomez <andreaxg@google.com>
Cr-Commit-Position: refs/heads/main@{#1180450}