LibGUI: Rename CallOnChange => AllowCallback and implement elsewhere

This is a helpful option to prevent unwanted side effects, distinguish
between user and programmatic input, etc. Sliders and SpinBoxes were
implementing it idiosyncratically, so let's generalize the API and
give Buttons and TextEditors the same ability.

Userland/Libraries/LibGUI/AbstractButton.cpp

@@ -44,7 +44,7 @@ void AbstractButton::set_text(String text)
     update();
 }
 
-void AbstractButton::set_checked(bool checked)
+void AbstractButton::set_checked(bool checked, AllowCallback allow_callback)
 {
     if (m_checked == checked)
         return;
@@ -71,7 +71,7 @@ void AbstractButton::set_checked(bool checked)
     }
 
     update();
-    if (on_checked)
+    if (on_checked && allow_callback == AllowCallback::Yes)
         on_checked(checked);
 }