Clouds don't work with WebGL2

[sanjeetsuhag]

As demonstrated in this Sandcastle, CloudCollection does not work when WebGL 2 is enabled due to a shader compilation error:

RuntimeError: Fragment shader failed to compile.  Compile log: ERROR: 0:5: '=' : global variable initializers must be constant expressions
ERROR: 0:6: '=' : global variable initializers must be constant expressions

[ggetz]

@sanjeetsuhag Is this a duplicate of #10739?

[sanjeetsuhag]

Ah, yep. It's a duplicate. Seems like #10739 is also a duplicate of #10064. I'll close the duplicates in favor of the oldest one.