Also cleanup moving methods around for reuse and so code can be more concise.
Removed some older references, where now we use `this.thread.x` or `this.output.x`.
Removed some older methods we no longer use (astFunctionPrototype).
Removed some overloaded functions from webgl1 and webgl2 glsl. We no longer need them.
Removed some references to `=== null` in favor of truthy. `if (undefined === null)` is true, and can lead to unexpected results, where we really wanted truthy, and is simpler to write.
