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/Session/session.cpp

@@ -485,7 +485,8 @@ void render(Session &s, std::uintptr_t client, const NativeFrame &local, std::ui
     // each frame.
     std::vector<NametagPlayer> nametags;
     const bool bubbles = s.chat_bubbles;
-    const bool labels = s.nametags || bubbles;
+    const bool names = s.nametags && !nametags_held_off.load(std::memory_order_relaxed);
+    const bool labels = s.nametags || bubbles; // (published even while names are held off, so none linger)
     if (labels) refresh_friends(s);
     // The newest chat lines from `sender` still inside the bubble duration, oldest first,
     // filtered the same way the chat panel filters them, each with the opacity it has left
@@ -821,7 +822,7 @@ void render(Session &s, std::uintptr_t client, const NativeFrame &local, std::ui
     if (labels)
         publish_custom_nametags(s.base, std::move(nametags),
                                 local.ready ? std::optional(local.pose.root.position) : std::nullopt,
-                                s.nametags, bubbles, s.chat_bubbles_distance, s.nametag_distance,
+                                names, bubbles, s.chat_bubbles_distance, s.nametag_distance,
                                 s.nametag_dots);
 }
 } // namespace