collision overall Part II - 50% coverage check

[adumesny]

Description

more fix for #1094 (part II of #1621)

• we now check for >50% coverage (using pixel drag vs target region) before
  we collide during a drag to replace
• this means we now support larger size swapping at their mid point.
  target is always used for mid point.

Note: web demo (#1094) is still not totally ideal as item 9 goes side way for some reason...

Checklist

• Created tests which fail without the change (if possible)
• All tests passing (yarn test)
• Extended the README / documentation, if necessary

[adumesny]

showing 50% coverage (sized 2 instead of 1 items)

20210219_225342.mp4

web demo (still some issues left, especially placing below)

20210219_225827.mp4

this stuff is HARD!!