keymap: Detect and report errors for uppercase keybindings (#27558)

Closes #25353

Detect keybindings using upper case instead of lowercase, and report an
error

Release Notes:

- N/A

crates/editor/src/test/editor_test_context.rs

@@ -240,7 +240,7 @@ impl EditorTestContext {
     // unlike cx.simulate_keystrokes(), this does not run_until_parked
     // so you can use it to test detailed timing
     pub fn simulate_keystroke(&mut self, keystroke_text: &str) {
-        let keystroke = Keystroke::parse(keystroke_text).unwrap();
+        let keystroke = Keystroke::parse_case_insensitive(keystroke_text).unwrap();
         self.cx.dispatch_keystroke(self.window, keystroke);
     }