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).

applications/utilities/surface/surfacePatch/surfacePatch.C

@@ -85,7 +85,7 @@ int main(int argc, char *argv[])
             IOobject::NO_WRITE
         ),
         meshDict.subDict("geometry"),
-        meshDict.lookupOrDefault("singleRegionName", true)
+        meshDict.getOrDefault("singleRegionName", true)
     );