This updates the VR Scene Inspection add-on with functionality for
loading and using default controller actions, including controller
poses and haptics, and visualizing VR controllers both in-headset and
in the regular 3D viewport.

In other words, users can finally view their VR controllers and use
them to navigate their scene in VR.

Controller actions (enabled by default) are available as an option in
the "VR Session" panel. For controller bindings that require OpenXR
extensions (Reverb G2, Vive Cosmos, Huawei), there is a new
"Action Maps" panel where users can toggle these bindings. Bindings
that require extensions are disabled by default since not all OpenXR
runtimes may support them, which will lead to an error during action
creation at session start.

There is also an option in the "Action Maps" panel to use a
gamepad (Xbox Controller) instead of motion controllers for VR
actions/viewport navigation.

In addition to default actions, this update adds new options for VR
controller visualization. For in-headset (VR) visualization, controller
visibility as well as style (dark/light, ray/no ray) can be set via the
"View" panel. For visualization in the regular 3D viewport, there is a
new option in the "Viewport Feedback" panel to draw controllers as
gizmos, similar to the existing option for the VR camera (headset).

Finally, this update also changes the VR Landmark "Custom Camera" type
to "Custom Object", so users can specify any object (not just cameras)
as a base pose reference, and adds a base scale option for custom
object and custom pose-type landmarks.

Reviewed By: Severin

Differential Revision: https://developer.blender.org/D11271