bpo-31985: Deprecate openfp in aifc, sunau, and wave (#4344)

bpo-31985: Deprecate openfp in aifc, sunau, and wave (#4344)

The openfp functions of aifp, sunau, and wave had pointed to the open
function of each module since 1993 as a matter of backwards
compatibility. In the case of aifc.openfp, it was both undocumented
and untested. This change begins the formal deprecation of those
openfp functions, with their removal coming in 3.9.

This additionally adds a TODO in test_pyclbr around using aifc.openfp,
though it shouldn't be changed until removal in 3.9.