Add conj! for arrays of arrays (JuliaLang#53303)

Apparently, `broadcast!(conj!, A, A)` is not allocation-free, so I
spelled it out, but perhaps there's a more elegant solution.

base/abstractarraymath.jl

@@ -119,6 +119,7 @@ julia> A
 """
 conj!(A::AbstractArray{<:Number}) = (@inbounds broadcast!(conj, A, A); A)
 conj!(x::AbstractArray{<:Real}) = x
+conj!(A::AbstractArray) = (foreach(conj!, A); A)
 
 """
  conj(A::AbstractArray)

test/arrayops.jl

@@ -2612,7 +2612,7 @@ end
 end
 
 @testset "sign, conj[!], ~" begin
- local A, B, C
+ local A, B, C, D, E
  A = [-10,0,3]
  B = [-10.0,0.0,3.0]
  C = [1,im,0]
@@ -2629,6 +2629,11 @@ end
  @test typeof(conj(A)) == Vector{Int}
  @test typeof(conj(B)) == Vector{Float64}
  @test typeof(conj(C)) == Vector{Complex{Int}}
+ D = [C copy(C); copy(C) copy(C)]
+ @test conj(D) == conj!(copy(D))
+ E = [D, copy(D)]
+ @test conj(E) == conj!(copy(E))
+ @test (@allocations conj!(E)) == 0
 
  @test .~A == [9,-1,-4]
  @test typeof(.~A) == Vector{Int}