[mlir][gpu] Add the Select Object compilation attribute.

**For an explanation of these patches see D154153.**

Commit message:
This patch adds the default offloading handler for GPU binary ops: `#gpu.select_object`,
it selects the object to embed based on an index or a target attribute, embedding
the object as a global string and launches the kernel using the scheme used in the
GPU to LLVM pass.

Depends on D154137

Reviewed By: mehdi_amini

Differential Revision: https://reviews.llvm.org/D154147