Add initial markdown preview to Zed (#6958)

Adds a "markdown: open preview" action to open a markdown preview.

https://github.com/zed-industries/zed/assets/18583882/6fd7f009-53f7-4f98-84ea-7dd3f0dd11bf


This PR extends the work done in `crates/rich_text` to render markdown
to also support:

- Variable heading sizes
- Markdown tables
- Code blocks
- Block quotes

## Release Notes

- Added `Markdown: Open preview` action to partially close
([#6789](https://github.com/zed-industries/zed/issues/6789)).

## Known issues that will not be included in this PR

- Images.
- Nested block quotes.
- Footnote Reference.
- Headers highlighting.
- Inline code highlighting (this will need to be implemented in
`rich_text`)
- Checkboxes (`- [ ]` and `- [x]`)
- Syntax highlighting in code blocks.
- Markdown table text alignment.
- Inner markdown URL clicks

crates/language/Cargo.toml

@@ -29,7 +29,7 @@ async-trait.workspace = true
 clock = { path = "../clock" }
 collections = { path = "../collections" }
 futures.workspace = true
-fuzzy = {  path = "../fuzzy" }
+fuzzy = { path = "../fuzzy" }
 git = { path = "../git" }
 globset.workspace = true
 gpui = { path = "../gpui" }
@@ -38,7 +38,6 @@ log.workspace = true
 lsp = { path = "../lsp" }
 parking_lot.workspace = true
 postage.workspace = true
-pulldown-cmark = { version = "0.9.2", default-features = false }
 rand = { workspace = true, optional = true }
 regex.workspace = true
 rpc = { path = "../rpc" }
@@ -55,6 +54,7 @@ text = { path = "../text" }
 theme = { path = "../theme" }
 tree-sitter-rust = { workspace = true, optional = true }
 tree-sitter-typescript = { workspace = true, optional = true }
+pulldown-cmark.workspace = true
 tree-sitter.workspace = true
 unicase = "2.6"
 util = { path = "../util" }