[java][DML EP] Modifying dml_provider_factory.h so it can compile as a C header file (#20157)
### Description
The dml_provider_factory header file can't be used in C programs as it
defines C++ inline operators. This PR rearranges that header file so
that it looks like valid C when used from C, and also makes a couple of
small modifications to the Java code so it correctly binds to the DML EP
at build time.
I'm having some difficulty testing it as I think it's pulling in the old
version of DirectML on my computer and I can't figure out what the
library loading path is in Java to make it look at the recent version I
downloaded. So the test I added fails with:
```
InferenceTest > testDirectML() FAILED
ai.onnxruntime.OrtException: Error code - ORT_RUNTIME_EXCEPTION - message: Exception during initialization: <path-to-ort>\onnxruntime\core\providers\dml\DmlExecutionProvider\src\AbiCustomRegistry.cpp(518)\onnxruntime.dll!00007FFF74819333: (caller: 00007FFF74793509) Exception(3) tid(4f58) 80070057 The parameter is incorrect.
at app//ai.onnxruntime.OrtSession.createSession(Native Method)
at app//ai.onnxruntime.OrtSession.<init>(OrtSession.java:74)
at app//ai.onnxruntime.OrtEnvironment.createSession(OrtEnvironment.java:236)
at app//ai.onnxruntime.OrtEnvironment.createSession(OrtEnvironment.java:221)
at app//ai.onnxruntime.InferenceTest.openSessionSqueezeNet(InferenceTest.java:1961)
at app//ai.onnxruntime.InferenceTest.runProvider(InferenceTest.java:665)
at app//ai.onnxruntime.InferenceTest.testDirectML(InferenceTest.java:657)
```
But it does correctly compile, and this error seems very similar to
other issues with the DML provider when it doesn't like a model due to
the loaded library being old. The test is using the squeezenet file
that's been in the repo since 2019. If someone can help me figure out
how to get the right version of DML in the library path I can test it
more on my end. I tried adding the folder with the new version into the
system path, but I'm not very familiar with Windows' library loading
behaviour.
### Motivation and Context
Fixes #19656 to allow use of the DirectML EP from ORT Java.
cc @martinb35