For text selection to work well it is important that `<hypothesis-text-word>`
elements do not span multiple lines. Previously the layout analysis only created
new words after a space. Since most lines end with a whole word, this was
sufficient in most cases. However this doesn't work if a word is broken across
multiple lines (eg. with a hyphen). To handle this case, also create a word
break if the current character does not vertically overlap the previous
character. This may create some false positives (ie. unnecessary word breaks),
but that doesn't harm text selection.

Fixes #5066