Support arbitrarily nested uniforms

[ValentinWalter]

Adds support for arbitrarily nested uniform values, e.g. a struct containing an array of some other struct.

The way Program was set up made this change trivial to implement, while simplifying code and removing assumptions.

[gordonnl]

Thanks for this, it looks clean! Although it seems uniform arrays break, eg:

uniforms = {
    uColors: {
        value: [color1, color2, color3, color4, color5],
    },
};

[ValentinWalter]

Should be working as expected now. (I'm not entirely sure whether I've tested every edge case.)

[gordonnl]

Thanks a lot for this. Sorry about the embarrassingly long delay, I finally got around to testing it