[LegalizeTypes] Add SoftenFloatRes_Unary and SoftenFloatRes_Binary functions...

[LegalizeTypes] Add SoftenFloatRes_Unary and SoftenFloatRes_Binary functions to factor repeated patterns out of many of the SoftenFloatRes_* functions

This has been factored out of D70654 which will add strict FP support to these functions. By making the helpers we avoid repeating even more code.

Differential Revision: https://reviews.llvm.org/D70736