Move from Zed fonts to IBM Plex (#13596)

Release Notes:

- Changed the default fonts to IBM Plex Sans and IBM Plex Mono. If you'd
like to go back to using Zed Sans/Zed mono you need to
[download](https://github.com/zed-industries/zed-fonts/releases/tag/1.2.0)
them and install them.

crates/recent_projects/src/dev_servers.rs

@@ -116,7 +116,7 @@ impl DevServerProjects {
 
         let markdown_style = MarkdownStyle {
             code_block: gpui::TextStyleRefinement {
-                font_family: Some("Zed Mono".into()),
+                font_family: Some("Zed Plex Mono".into()),
                 color: Some(cx.theme().colors().editor_foreground),
                 background_color: Some(cx.theme().colors().editor_background),
                 ..Default::default()