ENH: improve IOobjectList name filtering

- support name filtering by class based on <Type> or predicates.
  Eg,

      objects.sortedNames<volScalarField>(namePattern);
  vs  objects.sortedNames(volScalarField::typeName, namePattern);

  These can also be used directly for untyped name matching.
  Eg,
      objects.sortedNames<void>(namePattern);

  Can also use a predicate:

      objects.sortedNames(wordRe("vol.*Field"), namePattern);
      objects.sortedNames
      (
          [](const word& clsName){ return clsName.startsWith("vol"); },
          namePattern
      );