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

Texture2DDecoderNative/fp16.h

@@ -0,0 +1,36 @@
+#pragma once
+#ifndef FP16_H
+#define FP16_H
+
+#include "fp16/fp16.h"
+
+#endif /* FP16_H */
+
+/*
+ *
+ * License Information
+ *
+ * FP16 library is derived from https://github.com/Maratyszcza/FP16.
+ * The library is licensed under the MIT License shown below.
+ *
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2017 Facebook Inc.
+ * Copyright (c) 2017 Georgia Institute of Technology
+ * Copyright 2019 Google LLC
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated
+ * documentation files (the "Software"), to deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
+ * WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+ * OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ *
+ */