Make llvm::Error generated from replacement interfaces more specific.

Summary:
The new error information contains the type of error (e.g. overlap or bad file path)
and the replacement(s) that is causing the error. This enables us to resolve some errors.
For example, for insertion at the same location conflict, we need to know the
existing replacement which conflicts with the new replacement in order to calculate
the new position to be insert before/after the existing replacement (for merging).

Reviewers: klimek, bkramer

Subscribers: djasper, cfe-commits

Differential Revision: https://reviews.llvm.org/D26853

llvm-svn: 287639