Alert.js: Refactor code to match the other components
* Use this._element
* Remove handleDismiss method and keep its functionality on event
* Change JqueryInterface to be more generic
* Correct docs to be aligned with code, and add undocumented functionality
* Update alerts.md
Co-authored-by: XhmikosR <xhmikosr@gmail.com>
* Remove potential false positive assertions
querySelector() returns null but
expect(document.querySelector('...')).toBeDefined()
tests that the value is not undefined
* Migrated assertions from .toBeDefined() to .not.toBeNull() for .getInstance() calls in tests
* Migrate offcanvas assertions from .toBeDefined() to .not.toBeNull() for .getInstance() call
* convert more cases to not.toBeNull assertions
Co-authored-by: XhmikosR <xhmikosr@gmail.com>
