feat(gx): add incomplete 'CGxDeviceGLSDL' (#2)

* chore(build): add vendored SDL 3.0.0 library

* chore(build): add vendored glew-cmake-2.2.0 library

* feat(console): in the presence of -opengl launch flag, change GxApi to OpenGl

* feat(gx): add uncompleted CGxDeviceGLSDL targeting Windows and Linux

* chore(build): change SDL3 linkage from shared (bad) to to static (good)

vendor/sdl-3.0.0/include/SDL3/SDL_opengles2_gl2platform.h

@@ -0,0 +1,27 @@
+#ifndef __gl2platform_h_
+#define __gl2platform_h_
+
+/*
+** Copyright 2017-2020 The Khronos Group Inc.
+** SPDX-License-Identifier: Apache-2.0
+*/
+
+/* Platform-specific types and definitions for OpenGL ES 2.X  gl2.h
+ *
+ * Adopters may modify khrplatform.h and this file to suit their platform.
+ * Please contribute modifications back to Khronos as pull requests on the
+ * public github repository:
+ *      https://github.com/KhronosGroup/OpenGL-Registry
+ */
+
+/*#include <KHR/khrplatform.h>*/
+
+#ifndef GL_APICALL
+#define GL_APICALL  KHRONOS_APICALL
+#endif
+
+#ifndef GL_APIENTRY
+#define GL_APIENTRY KHRONOS_APIENTRY
+#endif
+
+#endif /* __gl2platform_h_ */