Fixes #2774.

There was a hardcoded standard in PSyclone where for matrix multiplications, the first one or two indices must be full ranges (i.e.: the Fortran would be written as matrix(:,:,...) or vector(:,...)). However, Fortran can perform matrix multiplications with the full ranges in different orderings, as long as the shape conforms.

When recent LFRic changes re-ordered some of the operator index accesses, this shifted the full ranges into forbidden permutations.

This change addresses this issue by allowing more permutations that produce valid Fortran matmul code.

Description of changes
Added a new private method _get_full_range_split to matmul2code_trans.py, which splits information about full range and non full range nodes as well as performs some validation. For a given array, the method iterates over the children, and checks whether or not they are Range nodes. If the Range node is a full range, we append its position in the array to a list. If not, we throw an error. If it is not a Range node then its position and the node itself are appended to two different lists.

After the children are iterated over, if we have more than two full ranges then this array is not a valid input for matmul, so we throw an error. Otherwise, return the two lists containing the positions of the full range and non full range nodes in the array, as well as the non full range node list.

Some further validation is performed to ensure that the first matrix involved in the matmul has exactly two full ranges, and that the second matrix has one or two (since it can be a vector or matrix).

The orderings and list of non full range nodes are fed to the modified _create_matrix_ref to make the matrix reference.

Testing
A new test test_apply_matmat_reordered has been added which tests the expected behaviour directly, by feeding the PSyIR some Fortran code with spatially conforming but re-ordered (with respect to the old standard) matrices. Other tests will be modified since a lot of them tested aspects of the old standard that no longer apply.