- Add `select_function` to `Platform` and implement it for `GenericCpu`
 - Add `SelectFunctions` AST pass

Squashed commit of the following:

commit e6b3aa856d2471b645f39d20673eb5259f7b1e1c
Author: Frederik Hennig <frederik.hennig@fau.de>
Date:   Wed Mar 27 17:15:55 2024 +0100

    add select_function stub to GenericGpu

commit 679428f053d6bfd3a5ba4d1d1ff6c903577e9ed3
Author: Frederik Hennig <frederik.hennig@fau.de>
Date:   Wed Mar 27 17:14:16 2024 +0100

    Remove IntrinsicsError in favor of MaterializaitonError. Move the latter to `backend.exceptions`.

commit 1a01cfde2f39b3394935c2a313312097d4cf66e0
Merge: d73d24c 0e4677de
Author: Frederik Hennig <frederik.hennig@fau.de>
Date:   Wed Mar 27 17:07:31 2024 +0100

    Merge branch 'backend-rework' into b_function_mat

commit d73d24cf038950f2129e717a43dd09df11d725c0
Author: Frederik Hennig <frederik.hennig@fau.de>
Date:   Tue Mar 26 18:19:08 2024 +0100

    introduce SelectFunctions and select_function protocol

co...

 - Add a `dtype` member to all expression nodes
 - Make the `Typifier` apply `dtype`s to all expressions
 - Adapt transformations and IterationSpace to set data types on created
   expressions
 - Refactor TypeContext and contextual typing interface to be more
   intuitive
 - Refactor the Typifier to apply more operations through the
   TypeContext

Squashed commit of the following:

commit 3e81188a318aa1dc294cf0cd11bf2ec7f62a9b55
Author: Frederik Hennig <frederik.hennig@fau.de>
Date:   Wed Mar 27 17:00:17 2024 +0100

    Improve typification of integer expressions

     - Check integer type constraint in `_apply_target_type` to correctly catch deferred expressions

commit 63d0cfa5ea1b8a41c9a74bbfcf0618fad03ffa48
Merge: 671f057 075ae357
Author: Frederik Hennig <frederik.hennig@fau.de>
Date:   Wed Mar 27 16:46:28 2024 +0100

    Merge branch 'backend-rework' into b_refactor_typing

commit 671f0578a39e452504243019dab28d93f0114082
Author: Frederik Hennig <frederik.hennig@fau.de>
Date:   Tue Mar 26 16:39:43 2024 +0100

    Fix documentation for Typifier and PsExpression

commit 3ec258517ad8a510118265184b5dc7805128dcd3
Author: Frederik Hennig <frederik.hennig@fau.de>
Date:   Mon Mar 25 17:14:21 2024 +0100

    Typing refactor:

      - Annotate all expressions with types
      - Refactor Typifier for cleaner information flow and better
        readability
      - Have iteration space and transformers typify newly created AST nodes

Integer functions

See merge request !368

Improve comment support

See merge request !367

  - remove DivFunc
  - Fix various imports
  - Move node_collection, isl, kernel_constraints_check to old