ENH: support predicate checks for argList (similar to dictionary methods)

- Favour use of argList methods that are more similar to dictionary
  method names with the aim of reducing the cognitive load.

  * Silently deprecate two-parameter get() method in favour of the
    more familiar getOrDefault.
  * Silently deprecate opt() method in favour of get()

  These may be verbosely deprecated in future versions.

applications/utilities/surface/surfaceBooleanFeatures/surfaceBooleanFeatures.C

@@ -1606,7 +1606,7 @@ int main(int argc, char *argv[])
 
 
     // Scale factor for both surfaces:
-    const scalar scaleFactor = args.get<scalar>("scale", -1);
+    const scalar scaleFactor = args.getOrDefault<scalar>("scale", -1);
 
     const word surf1Name(args[2]);
     Info<< "Reading surface " << surf1Name << endl;