There is way more reasons to interpolate a function into the
solution vector and we cover them with one code path:
* Dirichlet boundary conditions (strong ones)
* Initial conditions for instationary expressions
* Initial guesses for Newton solvers

To comply with latest pdelab.

It is badly implemented as is and does not offer value over
writing symbolic functions.

It is badly implemented as is and does not offer value over
writing symbolic functions.

Do not annotate FiniteElements anymore, further split driver code

Blockstructured tests may fail, since the interpolation of the exact solution is not suitable

Need to use handler from pymbolic as loopy codegen handlers
are too involved for standalone usage.

until poisson_neumann passes