Add combined link trail / link prefix parserTests case.

This protects against the bug fixed in https://gerrit.wikimedia.org/r/61512
which failed to process the rest of the paragraph after the first link
trail.

We also add more thorough test cases combining link trails, link prefixes,
and piped links.  This targets Parsoid round-tripping wikitext to wikitext
in particular.

Change-Id: I68fb3b2cec09906b19e6f833688a46b811ba9eb4
Merge "Add combined link trail / link prefix parserTests case."