Replace C++/CLI components with P/Invoke components (#562)

* Replace C++/CLI components with P/Invoke

* Deleted C++/CLI projects

* Use Utf8StringHandle to marshal UTF-8 strings

* Use plaform-default calling convention

* Handle DLL preloading on Linux and macOS

* Change intermediate and output directories of native projects

* Improve P/Invoke documentation

AssetStudioFBXNative/utils.cpp

@@ -0,0 +1,43 @@
+#include <fbxsdk.h>
+#include <cassert>
+
+#include "utils.h"
+
+Vector3::Vector3()
+	: X(0), Y(0), Z(0)
+{
+}
+
+Vector3::Vector3(float x, float y, float z)
+	: X(x), Y(y), Z(z)
+{
+}
+
+Quaternion::Quaternion()
+	: X(0), Y(0), Z(0), W(1)
+{
+}
+
+Quaternion::Quaternion(float x, float y, float z)
+	: X(x), Y(y), Z(z), W(1)
+{
+}
+
+Quaternion::Quaternion(float x, float y, float z, float w)
+	: X(x), Y(y), Z(z), W(w)
+{
+}
+
+Vector3 QuaternionToEuler(Quaternion q) {
+	FbxAMatrix lMatrixRot;
+	lMatrixRot.SetQ(FbxQuaternion(q.X, q.Y, q.Z, q.W));
+	FbxVector4 lEuler = lMatrixRot.GetR();
+	return Vector3((float)lEuler[0], (float)lEuler[1], (float)lEuler[2]);
+}
+
+Quaternion EulerToQuaternion(Vector3 v) {
+	FbxAMatrix lMatrixRot;
+	lMatrixRot.SetR(FbxVector4(v.X, v.Y, v.Z));
+	FbxQuaternion lQuaternion = lMatrixRot.GetQ();
+	return Quaternion((float)lQuaternion[0], (float)lQuaternion[1], (float)lQuaternion[2], (float)lQuaternion[3]);
+}