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.

assets/settings/default.json

@@ -50,6 +50,9 @@
   // Whether to pop the completions menu while typing in an editor without
   // explicitly requesting it.
   "show_completions_on_input": true,
+  // Whether to display inline and alongside documentation for items in the
+  // completions menu
+  "show_completion_documentation": true,
   // Whether to show wrap guides in the editor. Setting this to true will
   // show a guide at the 'preferred_line_length' value if softwrap is set to
   // 'preferred_line_length', and will show any additional guides as specified