onnxruntime

STFT for DML EP (#14736)

### Description
Implements the STFT operator for the DirectML execution provider. This
is implemented as a custom op, just like the DFT kernel, because it's
implemented as a composite of two operators (DML Mul/Identity + DFT). As
such, this inherits the same restrictions as the existing DFT kernel
(requires power-of-two window sizes for now).

This change also adds a native FP16 shader to DFT so that both DFT/STFT
kernels support float16 tensors. There is no typed UAV fallback or
emulation path, so the HW _needs_ to support native float16. It also
appears the stockham shader was compiled with all optimizations disabled
and debug symbols (tsk tsk, Sheil), and this has been fixed.

This is passing all existing STFT tests (i.e. all of 1). I'm adding some
additional collateral in the Windows AI conformance tests in parallel to
check some extra cases.

---------

Co-authored-by: Patrice Vignola <vignola.patrice@gmail.com>