Improve flag & option name quoting in completion generation for all 3 shells

[rgoldberg]

Improve flag & option name quoting in completion generation for all 3 shells.

Improve zsh quoting.

Many quoting issues remain.

To fix them, there should first be enforced & documented limits on the acceptable characters in various values throughout SAP to avoid unnecessary quoting (see #768).

Otherwise, there's a massive rabbit hole of quoting issues. Given the way that tests are currently setup, adding tests for a fixed issue in one shell requires the same issue to be fixed in all 3 shells, which is cumbersome.

e.g., I haven't ensured that fish's argparse function will work with shell characters that this PR now quotes. Beforehand, they would just break the whole script by causing syntax errors. Now, they might just mess up an option spec for argparse, which, while it could mess up argument parsing, will not cause syntax errors.

It will be a process of iterative improvement, rather than fixing everything at once.

Resolve #761

Checklist

• I've added at least one test that validates that my change is working, if appropriate
• I've followed the code style of the rest of the project
• I've read the Contribution Guidelines
• I've updated the documentation if necessary