Automate Function-by-Name and Function-by-Category Docs

[oleibman]

Examining whether it is possible to analyze the 2 Php scripts in the bin directory even though they lack a .php extension, I found that the docs generated by generate-document had not been updated in over a year even though support for a number of functions (e.g. ARRAYTOTEXT) had long ago been implemented. The files generated by the other script generate-locales are automatically generated as part of the unit test suite, and I can't see any reason not to do the same for generate-document.

It isn't totally clear that the 2 scripts in bin are needed any more now that each has an equivalent in the unit test suite. For now, I'm keeping them, and allowing them to be analyzed by phpcs, php-cs-fixer, and phpstan.

This is:

• a bugfix
• a new feature
• refactoring
• additional unit tests
• documentation

Checklist:

• Changes are covered by unit tests
  • Changes are covered by existing unit tests
  • New unit tests have been added
• Code style is respected
• Commit message explains why the change is made (see https://github.com/erlang/otp/wiki/Writing-good-commit-messages)
• CHANGELOG.md contains a short summary of the change and a link to the pull request if applicable
• Documentation is updated as necessary

Why this change is needed?

Provide an explanation of why this change is needed, with links to any Issues (if appropriate).
If this is a bugfix or a new feature, and there are no existing Issues, then please also create an issue that will make it easier to track progress with this PR.