A week's worth of fixes for indirect: - Added a `spawnprefab` editor-only command that allows to spawn (and pre-process) any prefab for testing. - Moved indirect ConVar stuff to a proper indirect_instancing.cs - Temporarily removed Core/* shaders from the compatibility list because indirect support is unclear. - Revamped the indirect compatibility decision logic to be more granular and robust. - Fixed invisible models when a renderer in instanceable but none of its materials are. - Fixed NRE when encoundering null materials. - Added TryEnqueueAdd which gives feedback about when enqueing a renderer failed due to incompatibility. - Downgraded assertion exception when a shader wasn't found to just a warning. - Reworked RejectReason structure to a struct fully interoperable with bool. - RustRenderer now remembers original shadow casting modes so that they can be restored when indirect rendering is disabled. - Store errors reported by TryEnqueueAdd in RustRenderer for debug purposes. - Automatically disable RustRenderer if object is a shadow proxy. - Automatically disable RustRenderer if any submeshes are incompatible with either indirect or fallback rendering.