support popup: a basic idea

[Decodetalkers]

Support popup in multiwindow

• give popup an unique id in layershellev, every time request a popup , finally pass this request to layershelllev, and generate a popup
• draw window in iced_layershell, and save a hashmap about the relation between uniqueid and iced::window::id, (lazy static)
• users can get if the id in view request is a popup, and who request it , draw the view of the popup
• handle the event of keyboard leave. when keyboard leave the surface, destroy the popup

[Decodetalkers]

add a new action in iced_layeshell, to request a popup window..

related logic is like
https://github.com/jjsullivan5196/wvkbd/blob/master/main.c#L622-L647

[Decodetalkers]

support xdg_base , popup both. layershell can conexist with other shell, maybe someone will have the request to open a normal setting window