Add convert to opposite case command (#11290)

crates/editor/src/editor.rs

@@ -5192,6 +5192,24 @@ impl Editor {
         self.manipulate_text(cx, |text| text.to_case(Case::Camel))
     }
 
+    pub fn convert_to_opposite_case(
+        &mut self,
+        _: &ConvertToOppositeCase,
+        cx: &mut ViewContext<Self>,
+    ) {
+        self.manipulate_text(cx, |text| {
+            text.chars()
+                .fold(String::with_capacity(text.len()), |mut t, c| {
+                    if c.is_uppercase() {
+                        t.extend(c.to_lowercase());
+                    } else {
+                        t.extend(c.to_uppercase());
+                    }
+                    t
+                })
+        })
+    }
+
     fn manipulate_text<Fn>(&mut self, cx: &mut ViewContext<Self>, mut callback: Fn)
     where
         Fn: FnMut(&str) -> String,