Merge ~xnox/software-properties:clickable-pro into software-properties:ubuntu/master

The root of the problem might be motivated by the whole width of the screen being allocated as selection area for the button. So if a URL is present, the question is: Does clicking the URL launch the URL or activate the radio button, or both?

Your workaround answers "both" to that question, which I guess is fine — I wonder how designers would answer —, but introduces a side effect of having a browser window or tab open for each time the radio button is selected, also when keyboard navigation is used; I think this is too high a price to pay. One could use Pango Layout's get_pixel_size to get the label width, get the x position of the mouse click and then decide if the click was on the link or not, but it seems too much work and maybe it cannot be made accurate (because maybe there is no way to get the x coordinates interval the link occupies), so I would rather do the hbox and possibly confuse screen readers.

Now, the hbox workaround would introduce another effect: the button selection area would no longer be {window width, radio button icon height} but {radio button icon width, radio button icon height}. So for consistency sake we would do the same for the other radio button too.

What do you think?

Exploring more of the *.ui options, it turns out accessibility directives are available; that mitigates or eliminates the concerns about screen readers.

E.g. by adding this to the radio button

                    <child internal-child="accessible">
                      <object class="AtkObject" id="magic_radio-atkobject">
                        <property name="AtkObject::accessible-name" translatable="yes">123</property>
                        <property name="AtkObject::accessible-description" translatable="yes">456</property>
                      </object>
                    </child>

The screen reader will say "123 selected radio button 456" when the first button is selected.

As such, I believe that hbox + accessibility directives is indeed the best approach to solve the issue at hand.