Popover components are not accessible

[jovyntls]

Tell us about your environment
MacOS Monterey 12.0.1

• MarkBind Version:
  v3.1.1

What did you do? Please include the actual source code causing the issue.
Create a popover component without a trigger component,
e.g. <popover content="Lorem ipsum dolor sit amet" triggers="focus">Popover on top</popover>

What did you expect to happen?
For accessibility purposes, the popover should be open-able from the keyboard to cater to keyboard-only users.

What actually happened? Please include the actual, raw output.
The popover content (in the above example, "Popover on top") is not focus-able by keyboard even when the triggers attribute is set to focus.
Furthermore, when a trigger method is not specified, currently MarkBind defaults to hover. However, this poses accessibility issues as hover is impossible to trigger for keyboard-only users.

Suggestion: Maybe we could set the default value of triggers to "hover focus"? This would maintain the expected hover behaviour, and also allow for accessibility for keyboard-only users. I think such a change would not be noticeable for most users, but would be helpful in terms of accessibility.

[ong6]

This issue exists on windows as well. I think Jovyn's solution makes sense and can be implemented.

[jovyntls]

I'll work on this after #1748 since there's some refactoring of the Popover/Tooltip components there!