Fix DropShadowFilter blur resolution on high-DPI renderers

[l8888888]

Fixes #327

Summary

• Add a resolution option to KawaseBlurFilter and pass it into the underlying Pixi filter
• Propagate DropShadowFilter pixel size and resolution into its internal KawaseBlurFilter
• Prevent the drop shadow blur pass from accidentally inheriting high devicePixelRatio render target sizes on Retina/iPhone renderers

Validation

• npm install --ignore-scripts (used because local canvas native install requires system graphics libs)
• npm run types
• npm run lint