BOM-418 TypeError: unhashable type: SequenceDescriptorWithMixins (#22051)
BOM-418 TypeError: unhashable type: SequenceDescriptorWithMixins (#22051)

DescriptorWithMixins are dynamically created and do not have a hash
class method. Those classes had hash values in python2 but do not
have a default hash in python3. Thus those class objects can not be
used as dict keys. Used location of section/unit instead of real object
for cache dict. Location object is hashable.
edx-solutions/edx-platform,edx/edx-platform,arbrandes/edx-platform,eduNEXT/edx-platform,EDUlib/edx-platform,eduNEXT/edunext-platform,stvstnfrd/edx-platform,eduNEXT/edx-platform,angelapper/edx-platform,cpennington/edx-platform,appsembler/edx-platform,edx/edx-platform,cpennington/edx-platform,appsembler/edx-platform,mitocw/edx-platform,msegado/edx-platform,eduNEXT/edunext-platform,edx-solutions/edx-platform,EDUlib/edx-platform,msegado/edx-platform,msegado/edx-platform,msegado/edx-platform,cpennington/edx-platform,edx-solutions/edx-platform,arbrandes/edx-platform,eduNEXT/edx-platform,stvstnfrd/edx-platform,mitocw/edx-platform,arbrandes/edx-platform,mitocw/edx-platform,appsembler/edx-platform,EDUlib/edx-platform,mitocw/edx-platform,edx/edx-platform,stvstnfrd/edx-platform,msegado/edx-platform,angelapper/edx-platform,appsembler/edx-platform,stvstnfrd/edx-platform,angelapper/edx-platform,eduNEXT/edunext-platform,cpennington/edx-platform,eduNEXT/edx-platform,eduNEXT/edunext-platform,edx-solutions/edx-platform,EDUlib/edx-platform,edx/edx-platform,arbrandes/edx-platform,angelapper/edx-platform