AdvancedGPUTextureUsage.TRANSIENT_ATTACHMENT (0x40) — when true, MSAA attachments can be
marked transient so TBDR drivers keep contents in tile memory and skip DRAM
allocation entirely. Not part of WebGPU 1.0; gated on the bit being present on
the GPUTextureUsage enum at runtime.
Optional WebGPU capabilities probed at adapter/device init.
Mirrors the WebGL renderer's WebGLExtensions pattern: each entry represents a feature, usage bit, or extension that may or may not be present in the current browser / adapter, and the renderer can check it at runtime before opting in.