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/OpenFOAM/db/functionObjects/functionObjectList/functionObjectList.C

@@ -797,7 +797,7 @@ bool Foam::functionObjectList::read()
 
             const dictionary& dict = dEntry.dict();
 
-            bool enabled = dict.lookupOrDefault("enabled", true);
+            bool enabled = dict.getOrDefault("enabled", true);
 
             newDigs[nFunc] = dict.digest();