* add API for glow point banks
Previously, a model API existed for glow points mounted on thrusters, but not glow points mounted on glow point banks. This adds glow point bank support. Also, this refactors and cleans up the implementation of the model API a bit.
* NULL -> nullptr
Indexes are a more robust way than pointers to manage model and submodel handles, and in the event that models are made dynamic in the future, indexes will be necessary anyway.
Several handle types in the scripting API used inheritance where composition would be more appropriate. This refactors those types, as well as removing the various handle types that were just aliases for `model_h`. These are just the C++-side types; all the Lua types remain as-is.
This also refactors `sound_h` to move the previous `isSoundValid` to `isValid` so that `ade_set_args` will work properly for sounds with the `Lua_API_returns_nil_instead_of_invalid_object` flag. The subclassing from `sound_entry_h` was removed and the "full validity check" was moved to `isValidWithEntry`. The Lua side remains unaffected, but additional documentation was added to clarify the usage.
Follow-up to #6009 and prerequisite to #6006 due to the `isValid` refactor for `sound_h`.
Allow scripts to reference submodels, submodel instances, and model instances. Currently just a few properties (like Orientation and Radius) can be accessed, but this can be easily expanded in the future.
Also add relevant functions to calculate real-world positions and orientations of rotated submodels.
Goober5000