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/field/fieldValues/surfaceFieldValue/surfaceFieldValue.C

@@ -876,7 +876,7 @@ bool Foam::functionObjects::fieldValues::surfaceFieldValue::read
 
     weightFieldName_ = "none";
     needsUpdate_ = true;
-    writeArea_ = dict.lookupOrDefault("writeArea", false);
+    writeArea_ = dict.getOrDefault("writeArea", false);
     totalArea_ = 0;
     nFaces_ = 0;
     faceId_.clear();