[ConfirmDialog] setCancelButton should set cancelable consistently

[sissbruecker]

Describe your motivation

When you set a custom cancel button, some overloads make the dialog cancelable automatically, while others do not:

• setCancelButton(String buttonText, ComponentEventListener<CancelEvent> cancelListener) - Cancelable
• setCancelButton(String buttonText, ComponentEventListener<CancelEvent> cancelListener, String theme) - Cancelable
• setCancelButton(Component component) - Not cancelable
• setCancelButton(Element element) - Not cancelable

Describe the solution you'd like

The behavior should be consistent, so either all methods make the dialog cancelable, or neither of them does. Same goes for setRejectButton.

Describe alternatives you've considered

No response

Additional context

No response

[yuriy-fix]

Methods shouldn’t change the cancelable state. If it’s false before setting, it should stay false, and if it’s true, it should remain true. Reject button should be changed accordingly.