[MLIR][OpenMP] Shifted hint from CriticalOp to CriticalDeclareOp

According to the OpenMP 5.0 standard, names and hints of critical operation are
closely related. The following are the restrictions on them:
 - Unless the effect is as if `hint(omp_sync_hint_none)` was specified, the
   critical construct must specify a name.
 - If the hint clause is specified, each of the critical constructs with the
   same name must have a hint clause for which the hint-expression evaluates to
   the same value.

These restrictions will be enforced by design if the hint expression is a part
of the `omp.critical.declare` operation.
 - Any operation with no "name" will be considered to have
   `hint(omp_sync_hint_none)`.
 - All the operations with the same "name" will have the same hint value.

Reviewed By: kiranchandramohan

Differential Revision: https://reviews.llvm.org/D112134