Evas GL shaders: Add mask 21, 12, 22 downsampling modes

Evas GL shaders: Add mask 21, 12, 22 downsampling modes

This is a huge patch, but keep in mind that 4326 line changes
were automatically generated from the template GLSL files.

This also adds some minor refactors here and there to accomodate
for the new shaders, but nothing crazy.

"GL fast-path" downsampled masks should now look pretty good.