Let clang-format move the cursor appropriately.

With this patch, clang-format will try to keep the cursor at the
original code position in editor integrations (implemented for emacs and
vim). This means, after formatting, clang-format will try to keep the
cursor on the same character of the same token.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@182373 91177308-0d34-0410-b5e6-96231b3b80d8