Allow collapsing disabled child widgets + sizing fixes

[miozune]

This is the code I used to test behaviors:

public ModularPanel buildUI(PosGuiData guiData, PanelSyncManager guiSyncManager, UISettings settings) {
    ModularPanel panel = new ModularPanel("test_tile");
    panel.child(new Rectangle().setColor(Color.RED.main).asWidget().alignX(0.5f).alignY(0.4f).size(1));
    Flow row = Flow.row();
    panel.child(row
            .center()
            .coverChildrenHeight()
            .width(150)
            .padding(2)
            // .paddingLeft(20)
            .collapseDisabledChild()
            .mainAxisAlignment(Alignment.MainAxis.SPACE_BETWEEN)
            .childPadding(3)
            .background(GuiTextures.DISPLAY)
            .child(new TestButton(row)
                    .overlay(IKey.str("1")))
            .child(new TestButton(row)
                    .overlay(IKey.str("2"))
                    .marginLeft(7))
            .child(new TestButton(row)
                    .overlay(IKey.str("3")))
            .child(new TestButton(row)
                    .overlay(IKey.str("4"))
                    .marginRight(7))
            .child(new TestButton(row)
                    .overlay(IKey.str("5"))));
    return panel;
}

private static class TestButton extends ButtonWidget<TestButton> {
    private TestButton(IWidget widget) {
        onMousePressed($ -> {
            setEnabled(false);
            if (NetworkUtils.isClient()) {
                WidgetTree.resize(widget);
            }
            return true;
        });
    }
}