popovers: Export user_sidebar_popped function in popovers.js.
popovers: Export user_sidebar_popped function in popovers.js.

This is a preparatory commit that exports user_sidebar_popped function
so that it can be used in hotkey.js for keyboard navigation support in
popover in right sidebar.

brainwane/zulip,kou/zulip,punchagan/zulip,brainwane/zulip,rht/zulip,eeshangarg/zulip,eeshangarg/zulip,brainwane/zulip,eeshangarg/zulip,hackerkid/zulip,showell/zulip,rht/zulip,andersk/zulip,hackerkid/zulip,eeshangarg/zulip,punchagan/zulip,hackerkid/zulip,zulip/zulip,eeshangarg/zulip,kou/zulip,rht/zulip,andersk/zulip,eeshangarg/zulip,andersk/zulip,hackerkid/zulip,rht/zulip,kou/zulip,hackerkid/zulip,zulip/zulip,rht/zulip,andersk/zulip,kou/zulip,punchagan/zulip,brainwane/zulip,kou/zulip,punchagan/zulip,punchagan/zulip,zulip/zulip,andersk/zulip,zulip/zulip,showell/zulip,showell/zulip,kou/zulip,showell/zulip,showell/zulip,hackerkid/zulip,punchagan/zulip,zulip/zulip,eeshangarg/zulip,brainwane/zulip,andersk/zulip,showell/zulip,rht/zulip,zulip/zulip,rht/zulip,punchagan/zulip,hackerkid/zulip,brainwane/zulip,showell/zulip,andersk/zulip,brainwane/zulip,kou/zulip,zulip/zulip