Changes

[ParserTest] Move raw string literal out of macro
Some combinations of gcc and ccache do not deal well with raw strings in 
macros. Moving the string out to attempt to fix the bots.

[ARM] Add and update FMA tests. NFC

[ARM] Fill in FP16 FMA patterns
This adds fp16 variants of all the fma patterns in the ARM backend.
Differential Revision: https://reviews.llvm.org/D72138

[ARM] Use isFMAFasterThanFMulAndFAdd for scalars as well as MVE vectors
This adds extra scalar handling to isFMAFasterThanFMulAndFAdd, allowing 
the target independent code to handle more folds in more situations (for 
example if the fast math flags are present, but the global 
AllowFPOpFusion option isnt). It also splits apart the HasSlowFPVMLx 
into HasSlowFPVFMx, to allow VFMA and VMLA to be controlled separately 
if needed.
Differential Revision: https://reviews.llvm.org/D72139