Planes platform support

Understand the AR Foundation capabilities implemented by the OpenXR Spatial Entities plane provider.

This package implements the following optional features of AR Foundation's XRPlaneSubsystem:

Feature	Descriptor Property	Supported
Horizontal plane detection	supportsHorizontalPlaneDetection	Yes
Vertical plane detection	supportsVerticalPlaneDetection	Yes
Arbitrary plane detection	supportsArbitraryPlaneDetection	Yes
Boundary vertices	supportsBoundaryVertices	Determined at runtime
Classification	supportsClassification	Determined at runtime
Plane Subsumption	supportsPlaneSubsumption	Determined at runtime

Plane subsumption support

Plane subsumption requires the XR_ANDROID_spatial_component_subsumed_by extension. If a runtime doesn't enable this extension, supportsPlaneSubsumption reports false and no plane reports a subsuming plane.

Refer to Handle subsumed planes to understand how your app can respond when a runtime subsumes one plane into another.