Autocomplete docs (#3126)

Release Notes:

- Added documentation display for autocomplete items.
- Fixed autocomplete filtering blocking the Zed UI, causing hitches and
input delays with large completion lists.
- Fixed hover popup link not firing if the mouse moved a slight amount
while clicking.
- Added support for absolute path file links in hover popup and
autocomplete docs.

Cargo.lock

@@ -2404,7 +2404,6 @@ dependencies = [
  "parking_lot 0.11.2",
  "postage",
  "project",
- "pulldown-cmark",
  "rand 0.8.5",
  "rich_text",
  "rpc",
@@ -3989,6 +3988,7 @@ dependencies = [
  "lsp",
  "parking_lot 0.11.2",
  "postage",
+ "pulldown-cmark",
  "rand 0.8.5",
  "regex",
  "rpc",