Tree: collapseAll() and other asynchronous methods resolve too early

[bill]

Running this code leaves the Tree closed rather than open, like it should.

mytree.collapseAll().then(function(){
	return mytree.set("paths", [
		["continentRoot", "AF", "SD", "Khartoum"],
		["continentRoot", "SA", "AR"]				// Argentina
	]);
});

Further, it's in a weird state, as clicking the icon on "Continents" doesn't open the Tree the first time. You need to click it twice.

Test case attached.

[bill]

sibling of Tree_a11y.html

[bill]

Root cause is #16431, either that ticket can be fixed, or Tree can workaround.

[bill]

In [30123]:

Fix problem where collapseAll() and other asynchronous Tree methods resolve too early. Fixes #16378, refs #16431 !strict.