[LibTooling] Add function to translate and validate source range for editing

Summary:
Adds the function `getRangeForEdit` to validate that a given source range is
editable and, if needed, translate it into a range in the source file (for
example, if it's sourced in macro expansions).

Reviewers: ilya-biryukov

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D64924

llvm-svn: 366469