gdk: Add GLES shaders

We cannot use GL shaders with GLES.

gdk/resources/glsl/gles2-texture.fs.glsl

@@ -0,0 +1,9 @@
+precision mediump float;
+
+uniform sampler2D map;
+
+varying highp vec2 vUv;
+
+void main() {
+  gl_FragColor = texture2D(map, vUv);
+}

gdk/resources/glsl/gles2-texture.vs.glsl

@@ -0,0 +1,10 @@
+attribute vec2 position;
+attribute vec2 uv;
+
+varying highp vec2 vUv;
+
+void main() {
+  vUv = uv;
+
+  gl_Position = vec4(position, 0.0, 1.0);
+}