The general rule is that comments start after their preceding
thread item, but when that is a heading we should skip past
the entire <h[1-6]> node to avoid making section edit links
part of the first comment.
Bug: T267988
Change-Id: Ia7f1b27e0a69a9aab7c7da743bf8549479304096
Expand the 'signatures-funny' test case with more examples, which
don't behave correctly.
Follow-up commits I04a8ea09401e06f2d4bb1f226f17eb528b29ed95 and
Ic26a87642f8a15d5de2f7073d4d8176b299c7f94 fix them.
Bug: T255738
Change-Id: I0fdd8bdf11b497ffeed37c37953c5730f6e4f3b7