Initially #82897 prevented
non-visible options from being rendered in the manual, but
visible-but-internal options were still being recursed into. This fixes
this, aligning the recurse condition here with the one in
make-options-doc/default.nix

This implements assertions/warnings supported by the module system directly,
instead of just being a NixOS option (see
nixos/modules/misc/assertions.nix).

This has the following benefits:
- It allows cleanly redoing the user interface. The new
  implementation specifically allows disabling assertions or
  converting them to warnings instead.
- Assertions/warnings can now be thrown easily from within
  submodules, which previously wasn't possible and needed workarounds.

…and co.

Previously this option was thought to be necessary to avoid infinite
recursion, but it actually isn't, since the check evaluation isn't fed
back into the module fixed-point.

Honestly this option should probably just be removed

Previously the .enable option was used to encode the condition as well,
which lead to some oddness:
- In order to encode an assertion, one had to invert it
- To disable a check, one had to mkForce it

By introducing a separate .check option this is solved because:
- It can be used to encode assertions
- Disabling is done separately with .enable option, whose default can be
  overridden without a mkForce

To avoid name clashes

Co-authored-by: Robert Hensing <robert@roberthensing.nl>

Module-builtin assertions, disabling assertions and submodule assertions