renderer/opengl: Extract shaders from source (#9600)

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Co-authored-by: Mihai Fufezan <mihai@fufexan.net>

src/render/shaders/glsl/tex.vert

@@ -0,0 +1,15 @@
+uniform mat3 proj;
+uniform vec4 color;
+attribute vec2 pos;
+attribute vec2 texcoord;
+attribute vec2 texcoordMatte;
+varying vec4 v_color;
+varying vec2 v_texcoord;
+varying vec2 v_texcoordMatte;
+
+void main() {
+    gl_Position = vec4(proj * vec3(pos, 1.0), 1.0);
+    v_color = color;
+    v_texcoord = texcoord;
+    v_texcoordMatte = texcoordMatte;
+}