Style language server name in completion menu

Omit in buffers with one or zero running language servers with the
capability to provide completions

Co-Authored-By: Antonio Scandurra <antonio@zed.dev>

crates/theme/src/theme.rs

@@ -775,6 +775,9 @@ pub struct AutocompleteStyle {
     pub selected_item: ContainerStyle,
     pub hovered_item: ContainerStyle,
     pub match_highlight: HighlightStyle,
+    pub server_name_container: ContainerStyle,
+    pub server_name_color: Color,
+    pub server_name_size_percent: f32,
 }
 
 #[derive(Clone, Copy, Default, Deserialize, JsonSchema)]