Add UITabInitializeEvent

[Xemuain]

Let to wrap UITab with additional functions.

@EventHandler
private void onUITabInitialize(UITabInitializeEvent event) {
    if (!(event.getTab() instanceof AccountsTab))
        return;

    event.setTab(new WrappedAccountsTab(event.getWindow()));
}

[RaphiMC]

What is your goal with this API? Do you want to full replace a tab or do you want to slightly modify a tab? Could you give an example how this API should be used. If you only want to modify the existing elements, you can do something like this:

final JPanel accountsTabPanel = RStream.of(ui.accountsTab).withSuper().fields().by("contentPane").get();
final JPanel body = (JPanel) accountsTabPanel.getComponent(0);

in the ViaProxyLoadedEvent

Here is a full example of my proposed way to modify the GUI contents (This example adds a new dropdown into the advanced tab): https://github.com/ViaVersionAddons/ViaProxyRakNetProviders/blob/main/src/main/java/net/raphimc/raknetproviders/RakNetProviders.java#L71

If you can't use this way of modifying the GUI let me know with an example of what you want to achieve and then I will consider adding a new event for that purpose