Move RangeMap.h into Utility

Summary:
This file implements some general purpose data structures, and so it
belongs to the Utility module.

Reviewers: zturner, jingham, JDevlieghere, clayborg, espindola

Subscribers: emaste, mgorny, javed.absar, arichardson, MaskRay, lldb-commits

Differential Revision: https://reviews.llvm.org/D58970

llvm-svn: 355509