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/mesh/manipulation/createPatch/createPatch.C

@@ -534,7 +534,7 @@ int main(int argc, char *argv[])
     #include "createTime.H"
 
     const word meshRegionName =
-        args.get<word>("region", polyMesh::defaultRegion);
+        args.getOrDefault<word>("region", polyMesh::defaultRegion);
 
     const bool overwrite = args.found("overwrite");