I encountered a case where I needed to know if an egui context menu was
open, even if the mouse cursor was not in an egui area (full details in
discord). I found that every resource I needed to detect that the menu
was open was either private, or pub(crate). While it is possible to
wrap the `Response::context_menu()` in code to do state-tracking, it
becomes necessary to duplicate that code in every place you use a
context menu.
In this commit, I add `Context::is_context_menu_open()`. Named similarly
to `Context::is_pointer_over_area()`, this method will return true if
any context menu is open. This is possible because the context menu
uses a temp var with a fixed Id to store its state. This method just
fetches the state, and interrogates it to see if there is a menu
present.
One helper method, `BarState::has_root()`, was added as all the fields
needed to perform the check were private to the `menu` module.
I've also updated the Context Menu demo to show the result of
`is_context_menu_open()` to verify the code functions as expected.
32a63da580