[mlir][Vector] Extend xfer_read(extract)->scalar load to support multiple uses

This patch extends the vector.extract(vector.transfer_read) -> scalar
load patterns to support vector.transfer_read with multiple uses. For
now, we check that all the uses are vector.extract operations.
Supporting multiple uses is predicated under a flag.

Reviewed By: hanchung

Differential Revision: https://reviews.llvm.org/D150812