Replace Bootstrap popover plugin with Floating UI

[matthew-white]

We use popovers in just a couple of ways in Frontend:

• Showing a QR code
  • FieldKeyList shows FieldKeyQrPanel in a popover.
  • FormDraftTesting shows FormDraftQrPanel in a popover.
• HoverCards shows a popover.

We want to do more with popovers. However, because of our use of the Bootstrap popover plugin, there are a number of limitations:

central-frontend/src/components/popover.vue

Lines 14 to 29 in 4158cd0

	The Popover component renders the content of a popover, then passes the
	resulting HTML to the Bootstrap popover plugin. That means that this component
	does not contain the popover content shown to the user; the actual popover
	content is a copy based on this component. This component is rendered, but
	hidden.
	This setup results in a few limitations:
	- The HTML passed to the Bootstrap plugin is not reactive, so the popover must
	be destroyed and reinitialized whenever its content changes. To do so, call
	the update() method.
	- We can't pass event handlers to the Bootstrap plugin, so don't use Vue event
	handling to listen for events. Instead, manually attach event listeners to
	the document and use event delegation.
	- Since the popover content is rendered here and also shown in the .popover
	element, avoid using an id attribute.

These limitations mean that it can be pretty unwieldy from a code perspective to add a popover. In contrast, it's pretty straightforward to add a modal.

This issue is to replace the Bootstrap popover plugin with something else. Moving away from Bootstrap plugins is something we want to do in general: see #984. I used Floating UI to implement our tooltips, and I liked it. I think we should take a look at how hard it would be to replace the Bootstrap plugin with Floating UI.

One issue to keep in mind is getodk/central#797. That issue requires fairly granular control of the placement of the popover. I think Floating UI would give us that control.

The Popover component wraps content that we want to show in a popover, similar to the Modal component. I like that component-based approach, so if there's a way to keep Popover similar to how it is today (in terms of its contract/API/props/slots), I think that'd be nice. However, we'd need to make a number of changes within Popover itself in order to replace the Bootstrap plugin.