[libTooling] Change Transformer's `cat` to handle some cases of text in macros.

Summary:
Currently, `cat` validates range selections before extracting the corresponding
source text. However, this means that any range inside a macro is rejected as an
error. This patch changes the implementation to first try to map the range to
something reasonable. This makes the behavior consistent with handling of ranges
used for selecting portions of the source to edit.

Also updates a clang-tidy lit-test for one of the checks which was affected by
this change.

Reviewers: gribozavr2, tdl-g

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D82126