Cleanup Core Dependencies

[bigtimebuddy]

We have tons of issues with peer dependencies, so this PR attempts to help simplify our network of peerDependencies, which has been caused numerous issues when folks upgrade. I think there's more follow-up work to do here, but I think this is a good first step.

Before

Before these were all peers of each other, the only exception being extensions which was added more recently as a core dependency.

• @pixi/core
  • @pixi/extensions
• @pixi/math
• @pixi/contants
• @pixi/utils
• @pixi/runner
• @pixi/settings
• @pixi/ticker

After

Now all the base packages are dependencies of core and core exports them. Users should now only import from @pixi/core.

• @pixi/core
  • @pixi/extensions
  • @pixi/math
  • @pixi/contants
  • @pixi/utils
  • @pixi/runner
  • @pixi/settings
  • @pixi/ticker

For instance:

import { Rectangle } from '@pixi/math';
import { settings } from '@pixi/settings';
import { ALPHA_MODES } from '@pixi/constants';

Now becomes:

import { Rectangle, settings, ALPHA_MODES } from '@pixi/core';

Summary

Overall, this change will also help improve developer experience and ecosystem plugins when extending PixiJS, as now these new core dependencies are opaque to users. While we still publish and organize these packages in our code-base, users only really need to be concerned about core.