Merge branch 'backend-rework' into fhennig/type-system-refactor

docs/source/backend/index.rst

docs/source/backend/transformations.rst

src/pystencils/backend/kernelcreation/ast_factory.py

src/pystencils/backend/kernelcreation/context.py

src/pystencils/backend/kernelcreation/iteration_space.py

src/pystencils/backend/transformations/__init__.py

src/pystencils/backend/transformations/canonical_clone.py

...ystencils/backend/transformations/canonicalize_symbols.py

...pystencils/backend/transformations/eliminate_constants.py

...ils/backend/transformations/hoist_loop_invariant_decls.py

src/pystencils/backend/transformations/reshape_loops.py

tests/nbackend/kernelcreation/test_iteration_space.py

tests/nbackend/transformations/test_canonical_clone.py

tests/nbackend/transformations/test_reshape_loops.py