[mlir][vector] Add lowering pattern for vector.warp_execute_on_lane_0 op

Add lowering of the vector.warp_execute_on_lane_0 into scf.if plus memory
transfer for the operands and yield values.

This also add an integration test running on GPU warp. The same tests can be
later re-used with different comment lines to tests distribution
transformations.

This is mostly from @springerm contribution.

Differential Revision: https://reviews.llvm.org/D125430