Text sparsification experiments
Put axes on top since marks can overflow (for now)
Improved culling
WIP on smart padding
Conflicts:
	src/main.ts
Perfect padding
Fix bug with visibility culling
Conflicts:
	src/culling.ts
Don't cull lines/areas
Don't cull for ordinal scales
Conflicts:
	src/culling.ts
Fix slowdown on Safari
Accommodate changes to Vega typing
Tweak constant