Simplify retrieval of target elements (with data-target and href)

Created by: pvdlg

Fixes #18641 (closed), fixes #21328 (closed).

Util.getSelectorFromElement is used to obtains the selector, (and later then the matching elements), referenced by data-target or href in JS components. If data-target is not defined it relies on a regex to determine if href is a selector or a regular link.

The problem is that there is no way to have a regex that will isolate URL from css selectors in 100% of the cases. For example href="div.class" can mean 'execute the JS action (collapse, dropdown, etc..) on all div with the class class or it can be a regular href URL redirecting to the page <context>/div.class

In order to solve this issue this PR remove the reliance on the regex and:

• replace getSelectorFromElement by getTargets that returns a JQuery with matching targets
• if data-target is defined, getTargets uses it
• if data-target is not defined, getTargets try to use href and considers it as the attribute containing the target selector, if a JQuery selection on it actually returns elements

In addition the PR slightly simplifies the code to retrieve targeted elements in each modules.

Currently if a JS module trigger element (i.e. element with data-toggle) doesn't have a valid selector in data-target nor in href nothing happen except for dropdown and alert in which the parent of the trigger is considered the target. There is no error reported and the JS module is bypassed and has no effect. I kept the same behavior in the PR.