Introduce a new FFMPEG frontend renderer: EGLRenderer

Right now this renderer works on X11 & Wayland with VAAPI as a backend.

Some rendering latency benchmarks on my `i7-10510U` (with
`intel-media-driver` 20.1.1 which cause a *huge* regression with the
SDL_Renderer):
|             | X11    | Wayland |
| Before      | 6.78ms | 22.50ms |
| EGLRenderer | 0.76ms | 00.77ms |

Signed-off-by: Antoine Damhet <antoine.damhet@lse.epita.fr>

app/shaders/egl.vert

@@ -0,0 +1,10 @@
+#version 300 es
+
+layout (location = 0) in vec2 aPosition; // 2D: X,Y
+layout (location = 1) in vec2 aTexCoord;
+out vec2 vTextCoord;
+
+void main() {
+	vTextCoord = aTexCoord;
+	gl_Position = vec4(aPosition, 0, 1);
+}