FR: Add default argument for Component::exitModalState() to not have to specify a return value

If I make a Component modal using juce::Component::enterModalState(), and then stop it being modal using juce::Component::exitModalState (...), I have to specify a return value to the exit method that’s not actually used (because, if I understand it correctly, the argument is only used for runModalLoop). This is very confusing in the code because I either have to have something like:

m_comp.exitModalState (0);

Which uses a magic number - not good. Or:

constexpr auto returnValue = 0;
m_comp.exitModalState (returnValue);

Which explains the magic number, but doesn’t make it clear that that number isn’t actually used. Sure I can add a comment to explain that but that’s kind of missing the point.

If exitModalState's argument had a default value I could have a much cleaner enter/exit pair of methods.

Pull request here: