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/solverInfo/solverInfo.C

@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2015-2016 OpenFOAM Foundation
-    Copyright (C) 2015-2019 OpenCFD Ltd.
+    Copyright (C) 2015-2020 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -148,7 +148,7 @@ bool Foam::functionObjects::solverInfo::read(const dictionary& dict)
         fieldSet_.read(dict);
 
         writeResidualFields_ =
-            dict.lookupOrDefault("writeResidualFields", false);
+            dict.getOrDefault("writeResidualFields", false);
 
         residualFieldNames_.clear();