Move to beginning or end of paragraph ignore `contenteditable="false"`

Ctrl+A/Ctrl+E are mac-specific key binding:
Ctrl+A: Move to the beginning of the line or paragraph.
Ctrl+E: Move to the end of a line or paragraph.

Consider this test case:
<div contenteditable>
  this <a contenteditable="false">link</a> after.|
</div>

Ctrl+A was pressed, the caret moved to the end of "link".
But the expected position of the caret is the beginning of the line.

Before this patch, `MoveToBeginning/EndOfParagraph` couldn't cross the
editing boundary. This patch changes `MoveToBeginning/EndOfParagraph`
to be able to cross the editing boundary.

Bug: 1511541
Change-Id: If427f2877f67930de64ed01cb7ae066616ec238c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5152397
Reviewed-by: Kent Tamura <tkent@chromium.org>
Reviewed-by: Siye Liu <siliu@microsoft.com>
Commit-Queue: Peng Zhou <zhoupeng.1996@bytedance.com>
Cr-Commit-Position: refs/heads/main@{#1335218}