[mlir][sparse] Fix rewriting for convert op and concatenate op.

Fix a problem in convert op rewriting where it used the original index for
ToIndicesOp.

Extend the concatenate op rewriting to handle dense destination and dynamic
shape destination.

Make the concatenate op integration test run on the codegen path.

Reviewed By: Peiming

Differential Revision: https://reviews.llvm.org/D138057