fix(menu): ensure init & drop is done on main thread

[amrbashir]

No description provided.

[jamischarles]

@amrbashir Is there any special way I should run this? When I run this branch with a very basic main.rs from create_tauri I get a stackoverflow...

warning: `app` (lib) generated 4 warnings
    Finished dev [unoptimized + debuginfo] target(s) in 6.81s

thread 'main' has overflowed its stack
fatal runtime error: stack overflow

When I ran lldb I found this

Process 60268 stopped
* thread #1, name = 'main', queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=2, address=0x16f606d78)
    frame #0: 0x00000001007a1f90 tauri-notes-app`tauri_runtime_wry::handle_user_message::h5d6c144da76d1f73(event_loop=0x0000000000000001, message=<unavailable>, context=UserMessageContext @ 0x000000016f608150, web_context=0x0000000123700000) at lib.rs:2165
   2162      webview_id_map: WebviewIdStore,
   2163    }
   2164
-> 2165    fn handle_user_message<T: UserEvent>(
   2166      event_loop: &EventLoopWindowTarget<Message<T>>,
   2167      message: Message<T>,
   2168      context: UserMessageContext,
Target 0: (tauri-notes-app) stopped.
(lldb) frame variable
(tauri_runtime_wry::Message<tauri::EventLoopMessage>) message = <variable not available>

(tauri_runtime_wry::UserMessageContext) context = {
  windows = strong=0, weak=4889537407 {
    value = borrow=0 {
      value = size=0
    }
  }
  webview_id_map = {
    0 = strong=0, weak=18446744073709551615 {
      data = <read memory from 0x13 failed (0 of 64 bytes read)>

    }
  }
}
(alloc::sync::Arc<std::sync::mutex::Mutex<std::collections::hash::map::HashMap<core::option::Option<std::path::PathBuf>, wry::web_context::WebContext, std::collections::hash::map::RandomState> > > *) web_context = 0x0000000123700000

[lucasfernog]

Doesn't really fix the issue but let's merge this anyway since this is a good approach to prevent weird behavior (and we won't be able to break the API later).