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/zed/Cargo.toml

@@ -59,6 +59,7 @@ project_panel = { path = "../project_panel" }
 project_symbols = { path = "../project_symbols" }
 quick_action_bar = { path = "../quick_action_bar" }
 recent_projects = { path = "../recent_projects" }
+release_channel = { path = "../release_channel" }
 rope = { path = "../rope"}
 rpc = { path = "../rpc" }
 settings = { path = "../settings" }