Components: Remove Popover isOpen prop, render by presence

[aduth]

This pull request seeks to refactor the Popover component to remove the isOpen prop and instead infer openness by its presence.

The goal with this change is that it avoids render logic of rendered children from being executed except when the Popover is in-fact visible, thus avoiding wasted render reconciliation.

Before:

<Popover isOpen={ isOpen }>Content</Popover>

After:

{ isOpen && <Popover>Content</Popover> }

Testing instructions:

Verify that there are no regressions in the behavior of any popovers, dropdown menus, and tooltips, including focus management (focus return, close on blur).

Ensure unit tests pass:

npm run test-unit

[youknowriad]

Tested several components and I can't find any noticeable regression.

Nice simplification 👍