This effect can scale Alpha values.
This is needed for testing Compositor, and coincidentally was requested
by a partner in the past. This also will generally be more useful in
full multi-asset, where we may want to have one input have different alpha
values than another
Also, update fragment_shader_copy_es2.glsl to not throw away alpha values.
This means ThumbnailStripShaderProgram (the only place this glsl is used) will
consider input alpha and output alpha appropriately
PiperOrigin-RevId: 555915092
0466bd7957