[Fix #1210] Fix false positive in UnneededPercentQ for %Q(\t")

We've said that %Q can be used for dynamic strings that contain
double quotes. Dynamic strings must include strings with special
characters such as \t and \n, not only strings with interpolation.
Make UnneededPercentQ spec easier to read

There were so many kinds of strings. It got complicated,
so a few heredoc strings are helpful, I think.
Fix false positive for heredoc strings in UnneededPercentQ
Merge pull request #1216 from jonas054/1210_fix_unneeded_pq

Fix UnneededPercentQ