Fix find(in(b), a) to return cartesian indices for matrix a

[nalimilan]

For consistency with find(x -> in(b), a).
Restrict function signatures for clarity, as a needs to support keys/pairs and these internal functions are only called on arrays and tuples.

Similar to #30102.

[garrison]

Thanks @nalimilan. Here is the example from Slack that led to this:

julia> findall(in([5, 6]), [5 6; 7 8])
2-element Array{Int64,1}:
 1
 3

julia> findall(!in([5, 6]), [5 6; 7 8])
2-element Array{CartesianIndex{2},1}:
 CartesianIndex(2, 1)
 CartesianIndex(2, 2)

julia> findall(x -> x in [5, 6], [5 6; 7 8])
2-element Array{CartesianIndex{2},1}:
 CartesianIndex(1, 1)
 CartesianIndex(1, 2)

[garrison]

CC @mbauman

Also: I agree that this is a minor change, but I do want to note that it is technically breaking AFAICT.

[KristofferC]

That is pretty much what the "minor change" label means.

[StefanKarpinski]

“Minor change” is a non-scary name for “technically breaking but unlikely to cause anyone real problems, which we will test by running PkgEval before releasing”.

[mbauman]

I just fixed the conflict — let's merge this before the feature freeze for 1.1.