[mlir] multi-argument binding for top-level transform ops

`applyTransforms` now takes an optional mapping to be associated with
trailing block arguments of the top-level transform op, in addition to
the payload root. This allows for more advanced forms of communication
between C++ code and the transform dialect interpreter, in particular
supplying operations without having to re-match them during
interpretation.

Reviewed By: shabalin

Differential Revision: https://reviews.llvm.org/D142559