window-list: App icon not shown on the taskbar

Some application can't show icon when working in wayland.
Use application state change signal to update app icon.

Fixes GNOME/gnome-shell-extensions#10
1 job for wip/xiaoguang/work-around-missing-icons in 3 minutes and 38 seconds (queued for 1 second)
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passed #3741
build-shell-extensions

00:03:38