Convert SemaDecl.cpp to pass callback objects to CorrectTypo.

Includes tests highlighting the cases where accuracy has improved
(there is one call that does no filtering beyond selecting the set
of allowed keywords, and one call that only triggers for ObjC code
for which a test by someone who knows ObjC would be welcome). Also
fixes a small typo in one of the suggestion messages, and drops a
malformed "expected-note" for a suggestion that did not occur even
when the malformed note was committed as r145930.

llvm-svn: 148420