WebNN: Support notEqual operator

This CL adds IDL and mojo definition of notEqual operator according to
the spec issue [1] and implements it on DirectML, CoreML and TFLite
backends.

This CL also fixes the implementation of element-wise binary in the
TFLite backend, where we missed to convert the output of some logical
operators (such as equal, greater and lesser etc.) from bool to uint8.

[1] webmachinelearning/webnn#375

Bug: 382526991,382527250,382526992
Change-Id: I1c782b030cf80e330f99fc0e6e7649d98c0a33d4
Cq-Include-Trybots: luci.chromium.try:win11-blink-rel, mac14.arm64-blink-rel, mac15.arm64-blink-rel, linux-blink-rel