ArrayContraction.split_multiple_contractions() should not split in case of diagonal matrix

[Upabjojr]

Consider the following code

from sympy.tensor.array.expressions.array_expressions import ArrayDiagonal, ArrayTensorProduct, ArrayContraction
from sympy.tensor.array.expressions.conv_array_to_matrix import convert_array_to_matrix

I = Identity(3)
A = MatrixSymbol("A", 3, 3)
B = MatrixSymbol("B", 3, 3)

expr1 = ArrayContraction(ArrayTensorProduct(A, B, I), (0, 2, 4))
expr2 = expr1.split_multiple_contractions()
# ===> ArrayContraction(ArrayTensorProduct(I, A, B), (0, 2), (1, 4))
expected = ArrayDiagonal(ArrayTensorProduct(A, B), (0, 2))
assert expr1.as_explicit() == expr2.as_explicit()
assert expr1.as_explicit() == expected.as_explicit()

The first assertion fails because expr2 is not equal to expr1 (on dimension has been contracted).

The expected result is given in the expected variable. Triple contraction with the identity matrix is equivalent to diagonalization (remember that PermuteDims may be necessary).