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/Plugins/plugin_host.cpp

@@ -316,6 +316,11 @@ void Host::follow_game() {
         }
     if (wants("events.skater"))
         for (const auto& launch : game.take_launches()) each([&](Plugin& plugin, const std::string&) { plugin.launched(launch); });
+    // The camera height button asking the plugin in its cycle to start or stop its camera.
+    for (const auto& news : game.take_camera_cycle())
+        each([&](Plugin& plugin, const std::string&) {
+            if (plugin.id() == news.plugin) plugin.game_event("camera_cycle", "camera", Json(news.enter ? "enter" : "leave"));
+        });
     // Touching (reskate.session.touch): the bodies read once for every plugin that has it on.
     {
         std::optional<std::vector<Body>> list;