Revert "Replace LinearAlgebra._iszero by Base.iszero" (#38764)

* Revert "Replace LinearAlgebra._iszero by Base.iszero (#36194)"

This reverts commit e7a1b99.

* add test

Author: simeonschaub

stdlib/LinearAlgebra/src/structuredbroadcast.jl

@@ -104,7 +104,9 @@ function isstructurepreserving(::typeof(Base.literal_pow), ::Ref{typeof(^)}, ::S
 end
 isstructurepreserving(f, args...) = false
 
-fzeropreserving(bc) = (v = fzero(bc); !ismissing(v) && iszero(v))
+_iszero(n::Number) = iszero(n)
+_iszero(x) = x == 0
+fzeropreserving(bc) = (v = fzero(bc); !ismissing(v) && _iszero(v))
 # Like sparse matrices, we assume that the zero-preservation property of a broadcasted
 # expression is stable.  We can test the zero-preservability by applying the function
 # in cases where all other arguments are known scalars against a zero from the structured

stdlib/LinearAlgebra/test/structuredbroadcast.jl

@@ -206,21 +206,7 @@ end
 
 end
 
-struct Zero end
-Base.iszero(::Zero) = true
-Base.zero(::Type{Zero}) = Zero()
-@testset "PR #36193" begin
-    z = Zero()
-    Z = [z z
-         z z]
-    zz = [z, z]
-    U = UpperTriangular(Z)
-    L = LowerTriangular(Z)
-    D = Diagonal(zz)
-    for a in [U, L, D]
-        @test identity.(a) isa typeof(a)
-        @test map(identity, a) isa typeof(a)
-    end
-end
+# structured broadcast with function returning non-number type
+@test tuple.(Diagonal([1, 2])) == [(1,) (0,); (0,) (2,)]
 
 end