[Flang][OpenMP][OpenACC] Add function for mapping parser clause classes with...

[Flang][OpenMP][OpenACC] Add function for mapping parser clause classes with the corresponding clause kind.

1. Generate the mapping for clauses between the parser class and the
   corresponding clause kind for OpenMP and OpenACC using tablegen.

2. Add a common function to get the OmpObjectList from the OpenMP
   clauses to avoid repetition of code.

Reviewed by: Kiranchandramohan @kiranchandramohan , Valentin Clement @clementval

Differential Revision: https://reviews.llvm.org/D98603