fix iOS 16.x version failed to pass MTLBinding's arg.used check

[junjie020]

It failed to pass this check:

bgfx/src/renderer_mtl.mm

Lines 1956 to 1957 in 4cb7b71

	if (arg.used)
	{

on:

• iOS 16.x version(won't be happend in iOS 17.x version)
• Queue Debugging option disable in XCode Scheme or launch App by touch the APP on the screen

My test devices are :
iPhone X with iOS version 16.7.6 and iPhone 8 Plus with iOS version 16.7.6
iPhone 15 pro with iOS version 17.2/17.4
iPhone SE3 with iOS version 17.2/17.4

The option Queue Debugging enable or not will affect MTLBinding's used value. If disable, it will always false; ortherwise true.

But in iOS 17.x, this value(MTLBinding.used) are always true.

This problem also relate to this issue:
##3116

I write this code to locate this problom:

bool findArgument(id<MTLBinding> b, NSArray<MTLArgument*>* arguments){
	const char* name = utf8String(b.name);
	for (MTLArgument *a in arguments){
		if (a.active && 0 == strcmp(utf8String(a.name), name)){
			return true;
		}
	}
	return false;
}

void checkArguments(NSArray<id<MTLBinding>> *bindings, NSArray<MTLArgument*>* arguments) {
	for (id<MTLBinding> b in bindings){
		assert(findArgument(b, arguments));
	}
}
void checkRelfectionArguments(RenderPipelineReflection reflection){
	checkArguments(reflection.vertexBindings, reflection.vertexArguments);
	checkArguments(reflection.fragmentBindings, reflection.fragmentArguments);
}

add this code before this line:

checkRelfectionArguments(reflection);

https://github.com/bkaradzic/bgfx/blob/master/src/renderer_mtl.mm#L2361

I found that reflection.vertexBindings / reflection.fragmentBindings is equal to reflection.vertexArgumens/reflection.fragmentArguments's MTLArgument with active is true

So, I think it's no need to check MTLBinding's used in ProcessArguments function.

[junjie020]

After few more test, this assumption is wrong:

So, I think it's no need to check MTLBinding's used in ProcessArguments function.

That test is: create a metal shader with a buffer, but not use it in this shader.
That not use value in MTLBinding.used will return false, also MTLArgument.active is the same value in iOS 17.x version.

That's my fault.