Add upper bound wildcard to HasComponents.add()

[mvysny]

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Describe your motivation

Say I have a List<Button>, I'd like to be able to call verticalLayout.add(buttons) but I can't: Java compiler says there's no add(List<Button>) function.

Describe the solution you'd like

The HasComponents.add() should be changed to add(Collection<? extends Component> components).

Workaround is to call add((Collection<Component>) buttons); but that emits a compiler warning, so it's not pretty.

Vaadin 24.3.3

[mshabarov]

Makes sense to do this 👍