No matrix operations for sub(SparseMatrixCSC, ..., ...)?

[pkofod]

Working on #15354 I realized that

A = rand(10, 10)
sA = sub(A, 1:10, 1:10)
sA'

works, but

As = sprand(10, 10, 0.3)
sAs = sub(As, 1:10, 1:10)
sAs'

does not. I would love to fix it, but I am wondering what the preferred way would be. Should I add a method in linalg/abstractsparse.jl, or?

Of course A' and As' works, but sA' seems to be redirected to the correct ctranspose, while sAs' does not get dispatched to the sparse method.

Edit: So I just realized that this goes for all matrix operations on subs of sparse matrices. Is this intentional? @andreasnoack

[simonster]

Related to #14398

[pkofod]

Seems both related, and a duplicate, thanks for the ref.

[timholy]

Coincidentally, I inadvertently fixed this in #15367.