doc/source/main_glossary.rst: Fix docs build errors

Some of the referenced terms within the glossary were not using the capitalization for which the term was declared.

I'm not sure why this is not failing in CI, but it is failing today on my host. Perhaps it depends on your host python or sphinx version, in any case ensuring that the :term: bla bla <Term Reference> matches the terms declared in the glossary in a case sensitive way fixes the build error.