[clang-format][NFC] Moved configuration parsing tests in own file

I want to reduce the size of ForatTest.cpp with its still wopping 25k
lines it is a burden on the compiler and editor (mine is clangd
powered).

This are tests which are really serving a different purpose than
formatting.

I've copied the code and made the following changes:
- Dropped the ; at the end of some macros, all macro "invocations"
  already have their own ;.
- Dropped the _F, we don't need a fxiture here.

Differential Revisison: https://reviews.llvm.org/D137823