Avoid lowering FacetNormal to ReferenceNormal in custom interface integrals

The aim of this PR is support for custom integrals in UFLACS.

Multimesh interface integrals on the inter-mesh boundary have quadrature rules provided at runtime. These rules consists of quadrature points and weights, as well as normal vectors at each quadrature point.

The effect of this PR is that for interface type custom integrals, FacetNormal is lowered to a new type QuadratureNormal instead of ReferenceNormal. This QuadratureNormal will take values provided at runtime.