[RDSD] Consolidate ways to get domain wildcard patterns

WebsitePreferenceBridge.toDomainWildcardPattern is already used to get
domain wildcard patterns when manually adding Request Desktop Site
domain settings via Add site dialog in Site settings.
This CL updated Request Desktop Site toggle in the app menu to use the
same method to get domain wildcard patterns.

Bug: 1367911
Change-Id: Ic7e306a9ea9cd6856a824891224c49ae2aa92f50
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3916237
Reviewed-by: Theresa Sullivan <twellington@chromium.org>
Reviewed-by: Christian Dullweber <dullweber@chromium.org>
Reviewed-by: Aishwarya Rajesh <aishwaryarj@google.com>
Commit-Queue: Shu Yang <shuyng@google.com>
Cr-Commit-Position: refs/heads/main@{#1051401}