Change the error message when `-split-input-file` is used with mlir-opt to...

Change the error message when `-split-input-file` is used with mlir-opt to make it recognizable by IDEs

By adding the line number of the split point immediately after the file
name (separated by `:`) this is recognized by various tool as a proper
location.

Ideally we would want to point to the line of the error, but that would
require some very invasive changes I suspect.

Reviewed By: jpienaar

Differential Revision: https://reviews.llvm.org/D93363