[webgpu] Bindgroups cache breaks down with init/uninit pattern.

[floooh]

When a sokol-gfx resource is re-created via the uninit/init calls (so the same sokol-gfx handle is used for a different underlying resource) the BindsGroup cache needs to be invalidated, otherwise WebGPU will rightfully complain about a 'destroyed resource' being submitted.

To reproduce: remove the .wgpu_disable_bindgroups_cache = true in the dyntex3d-sapp sample.