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/solvers/electromagnetics/mhdFoam/readBPISOControls.H

@@ -1,3 +1,3 @@
     const dictionary& Bpiso = mesh.solutionDict().subDict("BPISO");
 
-    const int nBcorr = Bpiso.lookupOrDefault<int>("nCorrectors", 1);
+    const int nBcorr = Bpiso.getOrDefault<int>("nCorrectors", 1);