Adding `iree.tensor.trace` support for printf debugging. (#16746)

Any tensor level op prior to or during flow can be annotated with the
`iree.tensor.trace` attribute to have `flow.tensor.trace` ops for all
tensor operands and results generated by the pass. The attribute can
either be a unit attr to have the trace key chosen automatically or a
string attr to specify it. We run the pass once at the head of the
pipeline prior to dispatch region formation and again once after, but
users can also slice out IR at any phase, add the attributes, use
iree-opt to run the pass, and pipe it back through the pipeline to
continue compilation.

This is printf debugging: it's not great, but it gets the job done.