[runtime] Simplify generated signatures by using native types.

[rolfbjarne]

There's no need to generate a 32-bit and 64-bit signature, because the binding
generator will automatically generate those based on any native types.

[monojenkins]

Build failure

[spouliot]

@rolfbjarne that's the same I tried earlier (and ping'ed you about). I also ran into the same issues as the bots.

[rolfbjarne]

@spouliot yeah, I tried to repro locally, but I didn't try the right test.

[rolfbjarne]

The problem here is the mix of a native enum and native types in the signature.

The generator produces:

if (IntPtr.Size == 8) {
	ret = global::ObjCRuntime.Messaging.xamarin_simd__Matrix4_objc_msgSendSuper_Int64_CGSize_nfloat_nfloat (this.SuperHandle, Selector.GetHandle ("projectionMatrixForOrientation:viewportSize:zNear:zFar:"), (Int64)orientation, viewportSize, zNear, zFar);
} else {
	global::ObjCRuntime.Messaging.xamarin_simd__Matrix4_objc_msgSendSuper_stret_int_CGSize_nfloat_nfloat (out ret, this.SuperHandle, Selector.GetHandle ("projectionMatrixForOrientation:viewportSize:zNear:zFar:"), (int)orientation, viewportSize, zNear, zFar);
}

the binding generator automatically generates signatures for the 32-bit and 64-bit types as well, which means that when declaring a signature containing nint, nfloat, nfloat the binding generator generates:

• nint_nfloat_nfloat
• int_float_float
• long_double_double

but if the first argument is a native enum, bgen generates calls to:

• int_float_float (Classic)
• int_nfloat_nfloat
• long_nfloat_nfloat

which doesn't match the binding generator does, thus the need for the manual int/long signatures instead of nint signatures for native types.