Bind groups with binding arrays with high max count in their bind group layout take an extremely long time to allocate descriptor sets for

[JMS55]

Description
Creating a bind group every frame with 3 binding arrays, each with a maximum count of 50_000 bindings in the bind group layout takes an unreasonable amount of time each frame. Note that I have less than 50 actual bindings in the bind group - the cost is scaling purely based on the bind group layout binding count. Setting it even higher, like 1million, results in insane times like 450ms.

Repro steps

1. Create a bind group layout like

BindGroupLayoutEntry {
    binding: 3,
    visibility: ShaderStages::COMPUTE,
    ty: BindingType::Buffer {
        ty: BufferBindingType::Storage { read_only: true },
        has_dynamic_offset: false,
        min_binding_size: None, // TODO
    },
    count: Some(unsafe { NonZeroU32::new_unchecked(50_000) }),
},
BindGroupLayoutEntry {
    binding: 5,
    visibility: ShaderStages::COMPUTE,
    ty: BindingType::Texture {
        sample_type: TextureSampleType::Float { filterable: true },
        view_dimension: TextureViewDimension::D2,
        multisampled: false,
    },
    count: Some(unsafe { NonZeroU32::new_unchecked(50_000) }),
}

2. Each frame, create a bind group based on this layout, with a binding array of a small number (<50) of buffers and textures.

Here's a C++ trace captured from Nsight, compressed via 7zip, and then into a zip because github won't let me upload 7z archives.
solari__2023_04_25__12_15_53 (2).zip

You need to be on a GPU that supports ray tracing. You can also run the code directly via cargo run --example solari from here https://github.com/JMS55/bevy/tree/solari, and see the code here https://github.com/JMS55/bevy/tree/solari/crates/bevy_solari/src/scene.

Misc
@danchia investigated and found that wgpu/gpu-descriptor was using the FREE_DESCRIPTOR_SET flag, which may be part of the cause https://github.com/zakarumych/gpu-descriptor/blob/413b91137138307afbede5bc918f77bae403493c/gpu-descriptor/src/allocator.rs#L278-L286. I'm not familiar enough with Vulkan to know.

Platform
Windows 11, Ryzen 5 2600, AdapterInfo { name: "NVIDIA GeForce RTX 3080", vendor: 4318, device: 8710, device_type: DiscreteGpu, driver: "NVIDIA", driver_info: "528.49", backend: Vulkan }

[JMS55]

Should probably be added to #3637

[cwfitzgerald]

This will be obsoleted by the creation of bind_group.update_bindings