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/editor/src/test.rs

@@ -25,7 +25,7 @@ pub fn marked_display_snapshot(
     let (unmarked_text, markers) = marked_text_offsets(text);
 
     let font = Font {
-        family: "Zed Mono".into(),
+        family: "Zed Plex Mono".into(),
         features: FontFeatures::default(),
         weight: FontWeight::default(),
         style: FontStyle::default(),