popovers: Export focus_first_popover_item function from popovers.js.
popovers: Export focus_first_popover_item function from popovers.js.

This commit is preparatory commit to adding support for keyboard
navigation by focusing om first menu item of all of our popovers. So
exporting focus_first_popover_item so that it can be reused in other
places.

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