Fix #119946: NLA stack decomposition doesn't work with bones

The issue was that the `PointerRNA` passed to `BKE_animsys_get_nla_keyframing_context`
needs to point to an `ID` which wasn't the case when keying bones.
That is because internally the `FCurve` path is used to resolve the property.
This can only work from the `ID` because the `FCurve` path is always stored relative to that.
While the function doesn't fail when the property can't resolve the path, it won't actually do
the remapping when passing it to `BKE_animsys_nla_remap_keyframe_values` later.

Pull Request: https://projects.blender.org/blender/blender/pulls/120008

source/blender/animrig/intern/keyframing.cc

@@ -949,9 +949,11 @@ void insert_key_rna(PointerRNA *rna_pointer,
   /* Keyframing functions can deal with the nla_context being a nullptr. */
   ListBase nla_cache = {nullptr, nullptr};
   NlaKeyframingContext *nla_context = nullptr;
+
   if (adt && adt->action == action) {
+    PointerRNA id_pointer = RNA_id_pointer_create(id);
     nla_context = BKE_animsys_get_nla_keyframing_context(
-        &nla_cache, rna_pointer, adt, &anim_eval_context);
+        &nla_cache, &id_pointer, adt, &anim_eval_context);
   }
 
   const float nla_frame = BKE_nla_tweakedit_remap(adt, scene_frame, NLATIME_CONVERT_UNMAP);

source/blender/blenkernel/BKE_animsys.h

@@ -238,7 +238,7 @@ typedef struct NlaKeyframingContext NlaKeyframingContext;
  *
  * \param cache: List used to cache contexts for reuse when keying
  * multiple channels in one operation.
- * \param ptr: RNA pointer to the Object with the animation.
+ * \param ptr: RNA pointer to the ID with the animation.
  * \return Keyframing context, or NULL if not necessary.
  */
 struct NlaKeyframingContext *BKE_animsys_get_nla_keyframing_context(

source/blender/blenkernel/intern/anim_sys.cc

@@ -3672,6 +3672,11 @@ void nlasnapshot_blend_get_inverted_lower_snapshot(NlaEvalData *eval_data,
 NlaKeyframingContext *BKE_animsys_get_nla_keyframing_context(
     ListBase *cache, PointerRNA *ptr, AnimData *adt, const AnimationEvalContext *anim_eval_context)
 {
+  /* The PointerRNA needs to point to an ID because animsys_evaluate_nla_for_keyframing uses
+   * F-Curve paths to resolve properties. Since F-Curve paths are always relative to the ID this
+   * would fail if the PointerRNA was e.g. a bone. */
+  BLI_assert(RNA_struct_is_ID(ptr->type));
+
   /* No remapping needed if NLA is off or no action. */
   if ((adt == nullptr) || (adt->action == nullptr) || (adt->nla_tracks.first == nullptr) ||
       (adt->flag & ADT_NLA_EVAL_OFF))