Fixing dump model ops feature on Windows for MGX EP

[urpetkov-amd]

Fixing dump model ops feature for MIGraphX EP on Windows. The feature wasn't functional because of saving format rules on Windows which are opposite from Linux.

Current state of the feature gives us opportunity to generate and save onnx model after subgraph optimizations before compiling it. On this way we can look how model graph looks like after optimizations and we can use the optimized model.

[snnn]

Yes, all files should be opened in binary mode.

Also, you should check if the file was closed successfully, which is another bug.

[urpetkov-amd]

Thanks.
Okay, should we merge this and do that in another PR or add to this one? @snnn

[urpetkov-amd]

@snnn

I added changes for this. I added check if file is open, if it's not successfully opened then we can throw an error, otherwise print a log. In this way check for closing is not necessary, it will be closed in the ofstream destructor after leaving the block.