Add toggle case command (#28415)

A small addition for those coming from JetBrain's IDEs. A behavioral
detail: when any upper case character is detected, the command defaults
to toggling to lower case.

> Note that when you apply the toggle case action to the CamelCase name
format, IntelliJ IDEA converts the name to the lower case.


https://www.jetbrains.com/help/idea/working-with-source-code.html#edit_code_fragments

Release Notes:

- Added an `editor: toggle case` command. Use `cmd-shift-u` for macOS
and `ctrl-shift-u` for Linux, when using the `JetBrains` keymap.

crates/editor/src/editor.rs

@@ -9143,6 +9143,17 @@ impl Editor {
         });
     }
 
+    pub fn toggle_case(&mut self, _: &ToggleCase, window: &mut Window, cx: &mut Context<Self>) {
+        self.manipulate_text(window, cx, |text| {
+            let has_upper_case_characters = text.chars().any(|c| c.is_uppercase());
+            if has_upper_case_characters {
+                text.to_lowercase()
+            } else {
+                text.to_uppercase()
+            }
+        })
+    }
+
     pub fn convert_to_upper_case(
         &mut self,
         _: &ConvertToUpperCase,