Implement SelectTree and SelectList as variable selectors in web-eda

[jernestmyers]

Requires this branch in web-eda.

DISCLAIMER: Much of this PR is representing outdated work towards the SingleSelect component and keyboard support that is up for review in this PR.

What's truly of note regarding implementation of these new components in web-eda is as follows:

• no changes were needed to implement SelectList
• to allow for more control in the SelectTree popover, I added a wrapPopover prop which works the same as the existing CheckboxTree's wrapper prop
• all other changes are either outdated work towards SingleSelect and keyboard support or CSS adjustments