Migration guide polish and examples

[sophschneider]

Fixes #10806

1. Added support for <details> toggles on markdown
2. Added support for collabsibleTOC pages (off by default) so you can quickly skip to the section you need. This isn't perfect yet (doesn't auto open when linking directly to an anchor) but is much better than what we currently have
3. Organized v11 to v12 styleguide into consistent steps
4. Put regex validation, mapping tables, and examples in details toggles to make the page less overwhelming and put migration commands at the forefront
5. Added introduction, glossary, and generalized the migration workflow section. Put these at the top to introduce builders to the migration
6. Added descriptive titles to all component migrations naming what they do
7. Added examples to each component migration and removed them from the "Whats new" page
8. Added regex validation snippets to all component migrations
9. Added alert text for stepped migrations that have to be run in order
10. Cleaned up copy and overall improved migration experience giving more context on how and why we are running the migrations. Aimed to make it clear enough that an intern could run a migration on their code base
11. Add padding to code blocks

[laurkim]

💯 🌟 🚀