Correct behavior of <syntaxhighlight highlight="[lines]"> with more than one line

• Restore parseHighlightLines() function from before 6484894497f59080eb3e62da4d11b658c84e19f4, which introduced a regression in parsing line ranges. There are no tests for this and I'm not going to debug the regexes.
• Use a space rather than a comma as separator when passing the list of line numbers to Pygments.

Bug: T85794
Change-Id: Ib86c216308a973000a4129c2c46286ec1dc988e1