Some QML properties access exposed Python objects that may or may not
be null upon their access. When these objects are accessed while null,
QML issues "TypeError" warnings. These warnings have no functional
impact as QML correctly handles trying to access null objects, but can
spam the logs.
This commit aims at fixing all these warnings by checking that the
Python objects are not null before being accessed.
Binding the "enabled" property of AlembicLoader's ObjectPicker to the parent MediaLoader's own "enabled" property caused invalid state where the loaded AlembicEntity was partially visible when toggling object visibility (since Qt 5.13).
In order to disable camera picking when AlembicEntity is disable, scale the camSelector component to 0.
This commit adds several components to centralize and extend 3D media loading. They are not yet integrated into Viewer3D. The entry point to this system is the MediaLibrary component that:
* can load N medias based on a filepath or load-and-watch node attributes
* provides a cache mechanism to instant-reload medias that were unloaded under certain conditions
* gives access to statistics (vertex/face/camera/textureCount) through a unified interface
