Move the sorting of code-completion results out of the main path and

Move the sorting of code-completion results out of the main path and
into the clients, e.g., the printing code-completion consumer and
c-index-test. Clients may want to re-sort the results anyway.

Provide a libclang function that sorts the results.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@112149 91177308-0d34-0410-b5e6-96231b3b80d8