[mlir][openacc] Update acc.loop to be a proper loop like operation (#67355)

The initial design of the `acc.loop` was to be an operation that
encapsulates a loop like operation. This was an early design and we now
want to change it so the `acc.loop` operation becomes a real loop-like
operation by implementing the LoopLikeInterface.

Differential Revision: https://reviews.llvm.org/D159229

This patch is just moved from Phabricator to github