In TypoCorrectionConsumer, BestResults to CorrectionResults to lessen

In TypoCorrectionConsumer, BestResults to CorrectionResults to lessen
the confusion among all of the uses of Best* in relation to the set of
possible typo correction results. Also add a method to return the set of
typo corrections that have the single best edit distance--it returns the
second half of the first pair in TypoEditDistanceMap (with
getBestEditDistance already returning the first half).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@157781 91177308-0d34-0410-b5e6-96231b3b80d8