Add jcheck whitespace checking for properties files

This is an attempt to finally implement the idea brought forward in JDK-8295729, which said:

Properties files is essentially source code. It should have the same whitespace checks as all other source code, so we don't get spurious trailing whitespace changes.

With the new Skara jcheck, it is possible to increase the coverage of the whitespace checks (in the old mercurial version, this was more or less impossible).

This turned out to be problematic, since trailing whitespace is significant in properties files. That issue has mostly been sorted out in a series of PRs, and this patch will finish the job with the few remaining files, and actually enable the check in jcheck.