onnxruntime

EP factory creation cleanup and enhancements. (#11798)

* Rework the EP factory creation setup so we're not cut-and-pasting function declarations in multiple places.
Convert append EP for SNPE to be generic, and also use for XNNPACK.
Add XNNPACK to C# API

* Don't need stub for MIGraphX as it's using provider bridge.

* Remove old 'create' functions that aren't applicable now that the EPs are built as separate libraries.

* Only use EPs that require the layout transform if the opset is supported by the layout transformer.

* Update wasm registration of xnnpack.