Move a few static functions from DiagnosticRenderer.cpp into SourceManager.

This simplifies the code a little bit, since these functions all took a
SourceManager parameter and called a bunch of methods on it, and makes
the functions available to other users.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@158676 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed