Change "Save Selection" command to Cmd+Alt+S (#2631)

Closes #2605
* #2605

### Checklist
* [x] I have read and agree to [Contributor
Guide](https://github.com/rerun-io/rerun/blob/main/CONTRIBUTING.md) and
the [Code of
Conduct](https://github.com/rerun-io/rerun/blob/main/CODE_OF_CONDUCT.md)
* [x] I've included a screenshot or gif (if applicable)
* [x] I have tested [demo.rerun.io](https://demo.rerun.io/pr/2631) (if
applicable)

- [PR Build Summary](https://build.rerun.io/pr/2631)
- [Docs
preview](https://rerun.io/preview/pr%3Aemilk%2Ffix-overlapping-keyboard-shortcuts/docs)
- [Examples
preview](https://rerun.io/preview/pr%3Aemilk%2Ffix-overlapping-keyboard-shortcuts/examples)

crates/re_ui/src/command.rs

@@ -164,8 +164,8 @@ impl UICommand {
         }
 
         #[cfg(not(target_arch = "wasm32"))]
-        fn cmd_shift(key: Key) -> KeyboardShortcut {
-            KeyboardShortcut::new(Modifiers::COMMAND.plus(Modifiers::SHIFT), key)
+        fn cmd_alt(key: Key) -> KeyboardShortcut {
+            KeyboardShortcut::new(Modifiers::COMMAND.plus(Modifiers::ALT), key)
         }
 
         fn ctrl_shift(key: Key) -> KeyboardShortcut {
@@ -176,7 +176,7 @@ impl UICommand {
             #[cfg(not(target_arch = "wasm32"))]
             UICommand::Save => Some(cmd(Key::S)),
             #[cfg(not(target_arch = "wasm32"))]
-            UICommand::SaveSelection => Some(cmd_shift(Key::S)),
+            UICommand::SaveSelection => Some(cmd_alt(Key::S)),
             #[cfg(not(target_arch = "wasm32"))]
             UICommand::Open => Some(cmd(Key::O)),
 
@@ -275,3 +275,43 @@ impl UICommand {
         }
     }
 }
+
+#[test]
+fn check_for_clashing_command_shortcuts() {
+    fn clashes(a: KeyboardShortcut, b: KeyboardShortcut) -> bool {
+        if a.key != b.key {
+            return false;
+        }
+
+        if a.modifiers.alt != b.modifiers.alt {
+            return false;
+        }
+
+        if a.modifiers.shift != b.modifiers.shift {
+            return false;
+        }
+
+        // On Non-Mac, command is interpreted as ctrl!
+        (a.modifiers.command || a.modifiers.ctrl) == (b.modifiers.command || b.modifiers.ctrl)
+    }
+
+    use strum::IntoEnumIterator as _;
+
+    for a_cmd in UICommand::iter() {
+        if let Some(a_shortcut) = a_cmd.kb_shortcut() {
+            for b_cmd in UICommand::iter() {
+                if a_cmd == b_cmd {
+                    continue;
+                }
+                if let Some(b_shortcut) = b_cmd.kb_shortcut() {
+                    assert!(
+                        !clashes(a_shortcut, b_shortcut),
+                        "Command '{a_cmd:?}' and '{b_cmd:?}' have overlapping keyboard shortcuts: {:?} vs {:?}",
+                        a_shortcut.format(&egui::ModifierNames::NAMES, true),
+                        b_shortcut.format(&egui::ModifierNames::NAMES, true),
+                    );
+                }
+            }
+        }
+    }
+}