[lldb] Introduce "RegInfoBasedABI"

Summary:
This patch creates a new subclass of the ABI class in order to abstract away the
mechanism in which we "augment" register information. This enables alternate
augmentation strategies to be introduced.

All existing ABI classes have been modified to inherit from RegInfoBasedABI, but
they will be refactored in subsequent patches.

Reviewers: JDevlieghere, jasonmolenda

Subscribers: sdardis, nemanjai, kbarton, jrtc27, atanasyan, jsji, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D74243