* Use MD LS for resolving all document links
This switches the markdown extension to use the markdown language service when resolving the link. This lets us delete a lot of code that was duplicated between the extension and the LS
* Pick up new ls version
* Markdown path completions tests use mocked out fs
This updates the path completion tests to stop depending on the actual fs and instead use `IMdWorkspace`
* Update remaining tests
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
For #140602
Only normal links for now. Will add reference links later. Should support the forms:
- `[](dir/file.md)`
- `[](./dir/file.md)`
- `[](/root-dir/file.md)`
- `[](#header)`
- `[](./dir/file.md#header)`
