Move TypoCorrection filtering into the TypoCorrectionConsumer and make it incremental.

The only external/visible functional change that fell out of this
refactoring is that there was one less case where the typo caching
and/or counting didn't work properly. The result is that a test case
had to be moved from typo-correction.cpp to typo-correction-pt2.cpp
to avoid the hard-coded limit on per file/TU typo correction attempts.

llvm-svn: 210669