Move margins to child views to not clip ChromeRefresh2023 focus frames

With ChromeRefresh2023, the focus frame around individual sources is
larger which resulted in it getting clipped for edge elements. By adding
extra margins to the child views instead of having it as insets of the
scroll view, this clipping is avoided.

Screenshots in crbug.com/1458860

Bug: 1422129, 1458860
Change-Id: I09f68d3821868596335ae53f94d9a4db07d0c26c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4649430
Reviewed-by: Elad Alon <eladalon@chromium.org>
Auto-Submit: Tove Petersson <tovep@chromium.org>
Commit-Queue: Tove Petersson <tovep@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1163601}