ENH: unify use of dictionary method names

- previously introduced `getOrDefault` as a dictionary _get_ method,
  now complete the transition and use it everywhere instead of
  `lookupOrDefault`. This avoids mixed usage of the two methods that
  are identical in behaviour, makes for shorter names, and promotes
  the distinction between "lookup" access (ie, return a token stream,
  locate and return an entry) and "get" access (ie, the above with
  conversion to concrete types such as scalar, label etc).

src/functionObjects/utilities/areaWrite/areaWrite.C

@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2019 OpenCFD Ltd.
+    Copyright (C) 2019-2020 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -139,7 +139,7 @@ bool Foam::areaWrite::read(const dictionary& dict)
         )
     );
 
-    verbose_ = dict.lookupOrDefault("verbose", false);
+    verbose_ = dict.getOrDefault("verbose", false);
 
     // All possible area meshes for the given fvMesh region
     meshes_ = obr().lookupClass<faMesh>();