Provide editor styling information separately from editor settings

* Since regular editors' font sizes and families are controlled by
  the settings and not the theme, don't store a dummy text style in
  the theme. Instead, only store a font color, and synthesize
  the text style for regular editors using both the theme and the
  settings.
* Style single-line and auto-height editors (now called "field
  editors") using a single function that takes the entire theme and
  selects a relevant sub-object.

Co-Authored-By: Nathan Sobo <nathan@zed.dev>

crates/workspace/src/settings.rs

@@ -72,4 +72,17 @@ impl Settings {
             .and_then(|settings| settings.preferred_line_length)
             .unwrap_or(self.preferred_line_length)
     }
+
+    #[cfg(any(test, feature = "test-support"))]
+    pub fn test(cx: &gpui::AppContext) -> Settings {
+        Settings {
+            buffer_font_family: cx.font_cache().load_family(&["Monaco"]).unwrap(),
+            buffer_font_size: 14.,
+            tab_size: 4,
+            soft_wrap: SoftWrap::None,
+            preferred_line_length: 80,
+            overrides: Default::default(),
+            theme: gpui::fonts::with_font_cache(cx.font_cache().clone(), || Default::default()),
+        }
+    }
 }