display DropdownButton menu on top of ProgressBubble

[davidsbailey]

Background

the "assign" menu for teachers has been appearing behind progress bubbles, as described in https://codeorg.axosoft.com/viewitem?id=1441&type=features&force_use_number=true .

The ProgressBubble has a high z-index so that its tooltip appears on top of other things, as explained in #19538 and here:

code-dot-org/apps/src/templates/progress/ProgressBubble.jsx

Lines 44 to 48 in 5f73df9

	// ReactTooltip sets a zIndex of 999. However, because in some cases for us
	// the ReactTooltip is inside of a rotated div, it ends up in a different
	// stacking context, and the zIndex doesn't work. Instead we set it here on
	// the top component
	zIndex: 999,

Description

Increase the z-index of the DropdownButton to more than that of the ProgressBubble . While we're at it, also increase the z-index of the teacher panel to make that appear on top of ProgressBubble too (see screenshots).

Screenshots

before

after