[iOS blink] iOS platform-specific rebaseline due to scrollbars - part3

We are observing differences in text expectations between MacPort and
iOSPort, specifically in aspects related to scrollbars.
Key differences include:
1. bounds diff of scrolling background of LayoutView #document
2. position and bounds diff of VerticalScrollbar/HorizontalScrollbar
3. "contentsOpaque" : true [1]
4. Scroll corner of LayoutNGBlockFlow [2]
These differences are a result related to the overlay scrollbar.
Unlike Mac, which doesn't use overlay scrollbar by default in web tests,
iOS uses it.
For more details, please refer to the following code references.
[1] https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/renderer/core/scroll/scrollbar.cc;drc=3050672c3dbc1f1aa9cf39dc9a0d904fac711930;l=887
[2] https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/renderer/core/paint/paint_layer_scrollable_area.cc;drc=556a639302edb38380da70a49cd31bff92658b06;l=1969

This CL has updated the rebaselining expectations for iOS
platform.

Bug: 1421239, 1504447
Change-Id: I5c5baef240d7af43ae9e610fa14aaa8843a02f66
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5183059
Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Reviewed-by: Ian Vollick <vollick@chromium.org>
Commit-Queue: Minju Kim <mkim@igalia.com>
Cr-Commit-Position: refs/heads/main@{#1247326}