Add dynamic exposure correction (#12959)

* Add uniform for frame delta time
* Adjust exposure in logarithmic (EV) space
* Add network support and LUA API
* Add testing mod

client/shaders/update_exposure/opengl_vertex.glsl

@@ -0,0 +1,11 @@
+#ifdef GL_ES
+varying mediump vec2 varTexCoord;
+#else
+centroid varying vec2 varTexCoord;
+#endif
+
+void main(void)
+{
+	varTexCoord.st = inTexCoord0.st;
+	gl_Position = inVertexPosition;
+}