[clang-format] Add simple macro replacements in formatting.

Add configuration to specify macros.
Macros will be expanded, and the code will be parsed and annotated
in the expanded state. In a second step, the formatting decisions
in the annotated expanded code will be reconstructed onto the
original unexpanded macro call.

Eventually, this will allow to remove special-case code for
various macro options we accumulated over the years in favor of
one principled mechanism.

Differential Revision: https://reviews.llvm.org/D144170