Support reversed Z rendering and float32 offscreen depth buffer

Combined, both options greatly improve camera depth accuracy compared to
OpenGL default Z mapping and int24 depth buffer.

Requires GL_ARB_clip_control and ARB_depth_buffer_float extensions

unity/Runtime/Bindings/MjBindings.cs

@@ -389,6 +389,14 @@ public enum mjtFramebuffer : int{
   mjFB_WINDOW = 0,
   mjFB_OFFSCREEN = 1,
 }
+public enum mjtDepthMapping : int{
+  mjDB_NEGONETOONE = 0,
+  mjDB_ONETOZERO = 1,
+}
+public enum mjtDepthPrecision : int{
+  mjDB_INT24 = 0,
+  mjDB_FLOAT32 = 1,
+}
 public enum mjtFontScale : int{
   mjFONTSCALE_50 = 50,
   mjFONTSCALE_100 = 100,