Improve dispatch of findall(testf::F, A::AbstractArray) (#46553)

This prevents some invalidations in `mightalias(A::AbstractArray, B::AbstractArray)`
in abstractarray.jl when loading Static.jl.

Here we specialize on the function instead of using map since
`broadcasting` returns a BitArray, `map` returns a Vector{Bool}.

Author: ranocha

base/array.jl

@@ -2325,7 +2325,7 @@ findall(testf::Function, A) = collect(first(p) for p in pairs(A) if testf(last(p
 
 # Broadcasting is much faster for small testf, and computing
 # integer indices from logical index using findall has a negligible cost
-findall(testf::Function, A::AbstractArray) = findall(testf.(A))
+findall(testf::F, A::AbstractArray) where {F<:Function} = findall(testf.(A))
 
 """
     findall(A)