ENH: support predicate checks for argList (similar to dictionary methods)

- Favour use of argList methods that are more similar to dictionary
  method names with the aim of reducing the cognitive load.

  * Silently deprecate two-parameter get() method in favour of the
    more familiar getOrDefault.
  * Silently deprecate opt() method in favour of get()

  These may be verbosely deprecated in future versions.

applications/utilities/postProcessing/dataConversion/foamToEnsight/foamToEnsight.C

@@ -357,7 +357,7 @@ int main(int argc, char *argv[])
 
     // Forced point interpolation?
     caseOpts.nodeValues(doPointValues && args.found("nodeValues"));
-    caseOpts.width(args.get<label>("width", 8));
+    caseOpts.width(args.getOrDefault<label>("width", 8));
     caseOpts.overwrite(!args.found("no-overwrite")); // Remove existing?
 
     // Can also have separate directory for lagrangian
@@ -366,7 +366,7 @@ int main(int argc, char *argv[])
     // Define sub-directory name to use for EnSight data.
     // The path to the ensight directory is at case level only
     // - For parallel cases, data only written from master
-    fileName outputDir = args.get<word>("name", "EnSight");
+    fileName outputDir = args.getOrDefault<word>("name", "EnSight");
     if (!outputDir.isAbsolute())
     {
         outputDir = args.globalPath()/outputDir;

applications/utilities/postProcessing/dataConversion/foamToVTK/foamToVTK.C

@@ -633,7 +633,8 @@ int main(int argc, char *argv[])
     else
     {
         regionNames.resize(1);
-        regionNames.first() = args.get<word>("region", fvMesh::defaultRegion);
+        regionNames.first() =
+            args.getOrDefault<word>("region", fvMesh::defaultRegion);
     }
 
 
@@ -695,7 +696,7 @@ int main(int argc, char *argv[])
     // Directory management
 
     // Sub-directory for output
-    const word vtkDirName = args.get<word>("name", "VTK");
+    const word vtkDirName = args.getOrDefault<word>("name", "VTK");
 
     const fileName outputDir(args.globalPath()/vtkDirName);