docs: use plugin names and refactor

[SethFalco]

To improve the usability and maintainability of our documentation, we're making the following changes:

• No longer using cleaned up names for plugins, instead we'll use the plugin ID as the title of the page, sidebar entry, and URL.
• The svgo.dev repository is now responsible for injecting the headings for each plugin page. This cleans up our docs a lot, and improves maintainability. (There had been a few instances where the headings were added incorrectly, such as forgetting to include the parameters heading for a plugin with parameters.)
• The implementation heading is being removed, and will now live in the TOC next to the "Edit this page on GitHub" link. This just looks a little cleaner.

Related

• Pairs with chore: automate plugin page headings svgo.dev#8