player hud: scripts can drive the hand animations, show empty hands and offset each hand (linked PR #4)

[TheLostInPlace]

LINKED PR # 4

This PR was split into a 4 part PR due to the size and to aid in reviewing changes

Changes

Script bindings on the player hud so a mod can move the hands without holding an invisible item.
While initially made with Wearable Devices in mind, nothing in it is tied/specific to
that mod.

• reads of the hud animation state, the freelook state, the hud fov and whether the hud is visible
• a position and rotation offset per hand with a blend time, game.set_hud_offset and
  game.clear_hud_offset, and script motions that keep playing while freelook is on
• a bare hands mode that draws the hands holding nothing, plus reading and setting the hands
  section
• a way to override the movement blend, and a full animation resync for scripts that swap hand
  models
• the hand motion tables are rebuilt when the hands model reloads, so a swapped model does not keep
  the old motions
• with bare hands up the attachment ui keeps drawing, and the frames skipped without hands are
  counted so a script can check
• two callbacks through callbacks_gameobject.script: actor_hud_on_script_anim_end (part,
  section, motion, reason) and actor_hud_on_hands_changed (new and old hands section)

Nothing changes unless a script calls the new functions, the bare hands mode is off by default.
Every new export is listed in lua_help_ex.script. Built DX11-AVX x64, tested in game with the
Wearable Devices mod. Merges into the MT branch without conflicts.