Renames in the markdown extension
This renames some types and splits up some files as part of an exploration towards a proper LSP. Changes:
- `SkinnyTextDocument` -> `ITextDocument`
- Moved `ITextDocument` to own file
- `MdWorkspaceContents` -> `IMdWorkspace`
This change reduces the number of times we retokenize a markdown file by doing the following:
- Use `MdTableOfContentsProvider` in more places
- Introduce a `IMarkdownParser` interface that lets us drop in a caching version of the tokenizer
This adds a command which renders the provided document, or the active
editor if one is provided. Following the pattern of some of the preview
commands, it returned `undefined` if there's no document provided and
no active text editor. Otherwise, seems to work...
```ts
const html = await vscode.commands.executeCommand<string>('markdown.render');
```
A way to render arbitrary strings in addition to documents may be useful at
some point in the future. However, I didn't implement that here as that'd
require some refactoring of the markdown engine. If we're interested though
I could certainly give that a shot.
