ENH: place more patch field attributes under template invariant Base

- attributes such as assignable(), coupled() etc

- common patchField types: calculatedType(), zeroGradientType() etc.
  This simplifies reference to these types without actually needing a
  typed patchField version.

ENH: add some basic patchField types to fieldTypes namespace

- allows more general use of the names

ENH: set extrapolated/calculated from patchInternalField directly

- avoids intermediate tmp

src/OpenFOAM/fields/pointPatchFields/basic/zeroGradient/zeroGradientPointPatchField.H

@@ -56,7 +56,7 @@ class zeroGradientPointPatchField
 public:
 
     //- Runtime type information
-    TypeName("zeroGradient");
+    TypeName("zeroGradient");  // fieldTypes::zeroGradientTypeName_()
 
 
     // Constructors