Plugins: what the Filmer needs as a plugin: carry, who sees a pose, a step in the camera cycle

PR 343's Filmer becomes a Luau plugin mod (kept in contrib/plugins/filmer) on general APIs instead of
its own C++:

- reskate.skater.carry: something held out in one or both hands and aimed, the body crouched (feet
  kept) and hunched over it, turned on the spot after it (Extension/Skater/carry.cpp, from the PR's
  filmer_hold.cpp, with tests)
- shown = "everyone" | "others" | "me" on skater.pose, reach and carry: the pose sent to the other
  players and the one drawn here are split when asked
- reskate.camera.cycle and the camera_cycle event: a plugin's camera as the last step of the camera
  height button's cycle, after first person
- reskate.session.nametags(false) holds the names over the other players off
- board.hide(bone, {others = true}) hides it in the board the others are sent too (a sent-pose filter)
- outfit.set takes hand wear slots; input.bind takes an action with no key of its own

Extension/Multiplayer/Remote/native_skater.cpp

@@ -556,6 +556,9 @@ NativeFrame capture_local(std::uintptr_t base, std::uintptr_t client, bool captu
         cache = {base, client, frame.context, player, frame.entity, frame.parent, component,
                  frame.board_entity};
         frame.ready = true;
+        // The pose as it is sent, after anyone who changes only what is drawn of the board has had it.
+        if (capture_pose)
+            if (const auto filter = shared().sent_pose_filter.load(std::memory_order_acquire)) filter(component, frame.pose);
     } catch (const std::exception &e) {
         cache = {};
         frame.detail = e.what();
@@ -612,6 +615,9 @@ void set_render_pose_listener(RenderPosePublished listener) noexcept {
 void set_animation_evaluated_listener(AnimationEvaluated listener) noexcept {
     shared().evaluated_listener.store(listener, std::memory_order_release);
 }
+void set_local_sent_pose_filter(LocalSentPoseFilter filter) noexcept {
+    shared().sent_pose_filter.store(filter, std::memory_order_release);
+}
 void set_local_pose_filter(LocalPoseFilter filter) noexcept {
     shared().pose_filter.store(filter, std::memory_order_release);
 }