Cleanup: move public doc-strings into headers for various API's

Some doc-strings were skipped because of blank-lines between
the doc-string and the symbol and needed to be moved manually.

- Added space below non doc-string comments to make it clear
  these aren't comments for the symbols directly below them.
- Use doxy sections for some headers.

Ref T92709

source/blender/blenkernel/intern/camera.c

@@ -756,7 +756,6 @@ static bool camera_frame_fit_calc_from_data(CameraParams *params,
   return false;
 }
 
-/* don't move the camera, just yield the fit location */
 bool BKE_camera_view_frame_fit_to_scene(
     Depsgraph *depsgraph, const Scene *scene, Object *camera_ob, float r_co[3], float *r_scale)
 {