Vector operators

This MR extends the HOG to enable the generation of vector-vector operators using the tensorial vector function spaces.

Those are relevant for two reasons:

• communication patterns should improve compared to "block-scalar" operators
• enables the implementation of certain forms that are not possible or at least complicated with scalar operators (e.g., Nitsche + free-slip BCs)

Still WIP until the following points are resolved:

• P1 support (first 2D results are looking good)
• P2 support
• 3D
• automated testing
• viscous ops with blending should be tested to make sure the full feature set is covered
• cleanup (check duplicated code in hyteg-coupling, forms, ...)

generate_all_operators.py

@@ -526,6 +526,7 @@ def all_operators(
     P1 = LagrangianFunctionSpace(1, symbolizer)
     P1Vector = TensorialVectorFunctionSpace(P1)
     P2 = LagrangianFunctionSpace(2, symbolizer)
+    P2Vector = TensorialVectorFunctionSpace(P2)
     N1E1 = N1E1Space(symbolizer)
 
     two_d = [TriangleElement()]
@@ -567,6 +568,24 @@ def all_operators(
 
     # fmt: on
 
+    p2vec_epsilon = partial(
+        epsilon,
+        variable_viscosity=True,
+        coefficient_function_space=P2,
+    )
+    ops.append(
+        OperatorInfo(
+            mapping=f"P2Vector",
+            name=f"Epsilon",
+            trial_space=P2Vector,
+            test_space=P2Vector,
+            form=p2vec_epsilon,
+            type_descriptor=type_descriptor,
+            opts=opts,
+            blending=blending,
+        )
+    )
+
     for c in [0, 1, 2]:
         # fmt: off
         div_geometries = [TriangleElement(), TetrahedronElement()]