Refactor and add tests for Popovers

[guerler]

This PR refactors the shared popper-based popover component by removing redundancies (50% less code), simplifying the code path and adding tests cases. This has the benefits that the behavior is much more predictable and reliable. It also makes additions and/or upcoming enhancements easier.

How to test the changes?

(Select all options that apply)

• I've included appropriate automated tests.
• This is a refactoring of components with existing test coverage.
• Instructions for manual testing are as follows:
  1. [add testing steps and prerequisites here if you didn't write automated tests covering all your changes]

License

• I agree to license these and all my past contributions to the core galaxy codebase under the MIT license.