Restructure documentation to reflect new compositional modifiers

[pokey]

We'd like to restructure out documentation to more accurately reflect Cursorless's new internal representation. We should have sections for:

• Scope types
• Modifiers
• Actions

They can link to each other. So for example the "containing scope" modifier can link to list of scope types

• [ ] Also discuss frontmatter thing for auto-generating docs

Scope types should include:

• [ ] Languages supported
• [ ] Examples from different languages
• [ ] Iteration scope
• [ ] Domain
• [ ] Removal range
• [ ] Content range

Could include info from test cases as per #866?

See also some (very rough 😅) images from a brainstorming session: