Updates to findmin/findmax: function application over multidims (#45061)
* Updates to findmin/findmax: function application over multidims
This adds support for findmin (and findmax) syntax: findmin(f, A;
dims). It is a natural extension of the extant findmin versions,
and required only small changes to the core algorithm (findminmax!).
However, it was necessary to redirect the 2-arg version in
reduce.jl in order to provide a single call site for
_findmin(f, A, :).