large number of items (>200) can be slow with float:false

[adumesny]

Subject of the issue

large number of items (>200) can be slow with float:false (very fast with float:true) - see many.html

https://github.com/gridstack/gridstack.js/blob/master/spec/e2e/html/1924-many.html

float:false is slow

https://user-images.githubusercontent.com/3496166/149815935-5f35098b-5c87-4e6e-9686-d15b02ae169c.mp4

both are relatively fast here

https://user-images.githubusercontent.com/3496166/149816030-2341bb44-c21a-4909-bc4d-0a4f938661f7.mp4