Define size for SVD (#28439)

* Define `size` for SVD

Closes #28438. And first PR!

* add test to 3-arg `ldiv!` on `SVD` which calls `size`

* github pampering

(cherry picked from commit e0876d2)

stdlib/LinearAlgebra/src/svd.jl

@@ -224,6 +224,9 @@ function ldiv!(A::SVD{T}, B::StridedVecOrMat) where T
     view(A.Vt,1:k,:)' * (view(A.S,1:k) .\ (view(A.U,:,1:k)' * B))
 end
 
+size(A::SVD, dim::Integer) = dim == 1 ? size(A.U, dim) : size(A.Vt, dim)
+size(A::SVD) = (size(A, 1), size(A, 2))
+
 # Generalized svd
 struct GeneralizedSVD{T,S} <: Factorization{T}
     U::S

stdlib/LinearAlgebra/test/svd.jl

@@ -29,6 +29,8 @@ using LinearAlgebra: BlasComplex, BlasFloat, BlasReal, QRPivoted
     # matrices from the factorization as expected.
     @test sf1.U*Diagonal(sf1.S)*sf1.Vt' ≊ m1
     @test sf2.U*Diagonal(sf2.S)*sf2.Vt' ≊ m2
+
+    @test ldiv!([0., 0.], svd(Matrix(I, 2, 2)), [1., 1.]) ≊ [1., 1.]
 end
 
 n = 10