feat(topology/connected.lean): add theorems about connectedness o… (#9633)
feat(topology/connected.lean): add theorems about connectedness o… (#9633)

feat(src/topology/connected.lean): add theorems about connectedness of closure

add two theorems is_preconnected.inclosure and is_connected.closure
	which formalize that if a set s is (pre)connected
	and a set t satisfies s ⊆ t ⊆ closure s,
	then t is (pre)connected as well
modify is_preconnected.closure and is_connected.closure
	to take these theorems into account
add a few comments for theorems in the code





Co-authored-by: Antoine Chambert-Loir <15f206c078d7b5fe2b55ab21afa852a198a85e7d@math.univ-paris-diderot.fr>
Co-authored-by: Oliver Nash <64b2b6d12bfe4baae7dad3d018f8cbf6b0e7a044@olivernash.org>

leanprover-community/mathlib,leanprover-community/mathlib