Convert globbed imports from PIXI to explicit package imports

[Bonkles]

Currently our code is sprinkled with

import * as PIXI from 'pixi.js';

we should REALLY convert these to explicit imports a la:

import {Container, Rectangle} from 'pixi';

The latter will allow esbuild to tree-shake more effectively and get rid of things we don't use.

[Bonkles]

Did some work on this today but it seems that we have some snags:

1. Resource loading doesn't work the same way apparently- the Promises being returned by the loader aren't including the 'textures' object which the helpers.js and others rely on.

2. The Pixi debugger chrome extension relies on a full bundle to be defined as PIXI

3. There were no bundle size savings even after doing it.

(stored on my local 'import_rework' branch)