[mlir] Adapted standard Alloc and Alloca ops to use new side-effect resources.

The current standard Alloca node is not annotated with the
MemEffect<Alloc> trait. This CL updates the Alloc and Alloca
memory-effect annotations using the latest Resource objects. Alloca
nodes will use a newly defined AutomaticAllocationScopeResource to
distinguish between Alloc and Alloca memory effects.

Differential Revision: https://reviews.llvm.org/D79620