[OpenMP][NFC] Move and simplify directive -> allowed clause mapping

Move the listing of allowed clauses per OpenMP directive to the new
macro file in `llvm/Frontend/OpenMP`. Also, use a single generic macro
that specifies the directive and one allowed clause explicitly instead
of a dedicated macro per directive.

We save 800 loc and boilerplate for all new directives/clauses with no
functional change. We also need to include the macro file only once and
not once per directive.

Depends on D77112.

Reviewed By: JonChesterfield

Differential Revision: https://reviews.llvm.org/D77113

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