Interactive shadows (#14702)

Co-authored-by: Ian Bassi <12130714+ianalexis@users.noreply.github.com>
Co-authored-by: Ian Bassi <ian.bassi@outlook.com>

resources/shaders/140/printbed_shadow.vs

@@ -0,0 +1,16 @@
+#version 140
+
+uniform mat4 view_model_matrix;
+uniform mat4 projection_matrix;
+
+in vec3 v_position;
+
+// The plate mask quad is authored directly in world coordinates (z = 0 plane),
+// so v_position is already the world position of the fragment.
+out vec4 world_pos;
+
+void main()
+{
+    world_pos = vec4(v_position, 1.0);
+    gl_Position = projection_matrix * view_model_matrix * vec4(v_position, 1.0);
+}