Add glossary and disambiguate cabal vs Cabal

[philderbeast]

Fixes #9976, by referring to glossary terms. Adds a glossary page to the users guide and links to it from the other pages.

For the styling, sets white-space: nowrap on table cells, to prevent glossary tables cells overflow. This applies only to tables with the wrap-cells class.

I'll squash commits before applying the merge label if this pull request is approved.

What's in it

• Alphabetical listing: with entries with synonyms placed together.
• Terms by category: Cabal-specific, Haskell-specific, and General tables.
• Easily confused terms: a table of terms that look alike or overlap with a sentence or two on how they differ.
• Links from other pages: :term: roles are linked at first use on a page but cabal and cabal-install are linked wherever they refer to the tool.

QA Notes

This is a doc-only change.

Running make users-guide should build the guide with no warnings.

---

• Patches conform to the coding conventions.
• Any changes that could be relevant to users have been recorded in the changelog.
  • Is the change significant? If so, remember to add significance: significant in the changelog file.
• The documentation has been updated, if necessary.
• Manual QA notes have been included.
• Tests have been added. (Not applicable: documentation only.)

[geekosaur]

In other places, cabal-install describes the package and cabal the command.

[philderbeast]

That is how it should be, isn't it? I've dropped uses of :term:`cabal-install:exe:cabal`.