gpui: Add Global marker trait (#7095)

This should prevent a class of bugs where one queries the wrong type of
global, which results in oddities at runtime.

Release Notes:

- N/A

---------

Co-authored-by: Marshall <marshall@zed.dev>
Co-authored-by: Marshall Bowers <elliott.codes@gmail.com>

crates/auto_update/src/update_notification.rs

@@ -3,7 +3,7 @@ use gpui::{
     SemanticVersion, StatefulInteractiveElement, Styled, ViewContext,
 };
 use menu::Cancel;
-use util::channel::ReleaseChannel;
+use release_channel::ReleaseChannel;
 use workspace::ui::{h_flex, v_flex, Icon, IconName, Label, StyledExt};
 
 pub struct UpdateNotification {
@@ -14,7 +14,7 @@ impl EventEmitter<DismissEvent> for UpdateNotification {}
 
 impl Render for UpdateNotification {
     fn render(&mut self, cx: &mut gpui::ViewContext<Self>) -> impl IntoElement {
-        let app_name = cx.global::<ReleaseChannel>().display_name();
+        let app_name = ReleaseChannel::global(cx).display_name();
 
         v_flex()
             .on_action(cx.listener(UpdateNotification::dismiss))