As a result of 0fc71f60cd, "empty" text
nodes (containing only whitespace) at the end of the comment may be
inside the comment's range, and trying to ignore them caused the
ranges not to match and the frame not to be detected.
Now the code works whether they're inside the comment's range or not.
Add a test case for wrapped discussion comments with HTML comments and
with whitespace.
Bug: T250126
Bug: T268407
Change-Id: I2217ff5a635fd1c9c9e803f46795b1bfb3d17535
