Components `getInstance` should be able to resolve string selectors and jQuery objects as the componnent constructor

Our Components constructor accepts HTMLElement | css-selector | jQuery object and resolves it to HTMLElement

https://github.com/twbs/bootstrap/blob/34db122ecce249c81a519dbcb4caf42dac58460e/js/src/base-component.js#L23-L25

In the opposite way, getInstance accepts only HTMLElement

https://github.com/twbs/bootstrap/blob/34db122ecce249c81a519dbcb4caf42dac58460e/js/src/base-component.js#L50-L53

It would be more consistent getInstance to support multiple types of argument too