…ectness issue with Mergesort (only)

…im-mutable-arrays

Professor Borkowski fixed these issues:
 - Merge sort works on all backends
 - Quick sort works on all backends
 - The property test that swap is commutative now passes

Remaining known issues with mutable backends:
 - splitMid returns arrays with changed elements
 - Swapping an index with itself changes the element at that index
 - makeArray doesn’t initialize elements to the proper value

The test cases incorrectly assumed that makeArray initializes elements on
the mutable backends and that fromList is defined for size 0.
This commit updates the test suite to account for these issues by:

 - Removing tests that makeArray initializes elements for mutable backends.
 - Using replicate and fromList in splitMid tests to initialize elements.
 - Copying arrays when testing the commutativity of swaps.
 - Removing 0 from the range of fromList calls.

There is still one failing test. This is the test for swapping the same index,
which only fails on the prim-mutable-arrays backend.

Other changes:
 - Replace type annotations with type applications to improve readability.
 - Set the default-language of the test suite to GHC2021.