opengl: fix transform order

The TransformMatrix is provided by Android to apply its internal
coordinates transformations to sample the texture at the correct
location, so it must be applied last, after the orientation/crop from
the picture_t.

The fact that their internal transform is exposed as an explicit matrix
is an arbitrary design choice from Android. Instead they could have
exposed a GLSL function "android_texture2D(vec2 coords)":

    vec2 tex_coords = TexCoordsMap * OrientationMatrix * pic_coords;
    vec4 texel = android_texture2D(tex_coords);

In that case, it is obvious that their transform would be applied last.

Refs <https://developer.android.com/reference/android/graphics/SurfaceTexture#getTransformMatrix(float%5B%5D)>