chore(data/fintype/basic): rename some instances (#11845)
chore(data/fintype/basic): rename some instances (#11845)

Rename instances from `infinite.multiset.infinite` etc to
`multiset.infinite` etc; rename `infinite.set.infinite` to
`infinite.set` to avoid name clash.

Also add `option.infinite`.





leanprover-community/mathlib,leanprover-community/mathlib