GPv3: Conversion: Initial animation handling.

Add generic handling of all potential FCurves, with custom callbacks to
perform the actual conversion (typically, some RNA paths will need to
be updated).

Currently implements only remapping of modifiers' animation.

This commit only handles Object-level animations, not sure whether
GreasePencil data also needs to be covered?

@@ -6,6 +6,12 @@
  * \ingroup bke
  */
 
+#include <functional>

@@ -7,2 +7,4 @@
  */
 
+#include <functional>
+#include <iostream>

@@ -620,0 +696,4 @@
+  /* Convert animation data if needed. */
+  AnimData *anim_data = BKE_animdata_from_id(&object.id);
+  if (anim_data) {
+    auto modifier_path_update = [&](FCurve *fcurve) -> bool {

@@ -40,3 +46,4 @@
 
 namespace blender::bke::greasepencil::convert {
 
+/**************************************************************************************************

@@ -43,0 +52,4 @@
+ * These utils will call given callback over all relavant fcurves (also includes drivers, and
+ * actions linked through the NLA).
+ *
+ * Note that by using `std::bind`, it is possible to pass more contextual data to a specific

@@ -620,0 +710,4 @@
+      const std::string new_rna_path = fmt::format(
+          "modifiers[\"{}\"]{}", new_md.name, rna_path.substr(int64_t(legacy_root_path.size())));
+      MEM_freeN(fcurve->rna_path);
+      fcurve->rna_path = BLI_strdup(new_rna_path.c_str());