Ensure clean shutdown of JS threads
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FIX https://github.com/servo/servo/issues/26685
FIX https://github.com/servo/servo/issues/26996
FIX https://github.com/servo/servo/issues/9672FIX#27027
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Support for webxr layer management
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This adds layer management to servo's webxr implementation, and removes all the special-cased code for openxr surface creation and opaque framebuffers.
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Implement GPUBuffer.mapAsync and update wgpu-core
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This PR covers the following-
1. update wgpu-core to use serializable `RenderPass` and `ComputePass`. Implement `DispatchIndirect`.
2. Implement `GPUBuffer.mapAsync()`.
The `mapAsync()` methods has the following flow-
1. A new promise is created in `mapAsync()` and a message sent to the server-side. This returns a promise.
2. On the server-side, a `struct BufferMapInfo` object stores the relevant info required to send data to the client-side on completion of mapping. This object is stored in a `buffer_maps: HashMap<id::BufferId, BufferMapInfo<'a>>,` in `WGPU`. `buffers_maps` basically stores the data for buffers with pending mapping.
3. `buffer_map_async()` command is issued with a callback responsible to send the data back to the client.
4. All the devices are polled every time the server receives a new message.
5. The data is sent back on completion and promise resolved through `AsyncWGPUListener` (similar to how the `requestDevice()` and `RequestAdapter` are processed).
6. On receiving the data, the client sends back a `BufferMapComplete` message to the server to remove the entry from `buffer_maps` hashmap.
I intended to implement `getMappedRange()`, too, in this PR but it's quite a task in itself (implementing intersecting ArrayBuffers). This already being a 500+ line PR, I thought it best to get this model approved first (also it will probably be easier to review this and `getMappedRange` separately). `getMappedRange` would come up in the next one.
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Update winapi
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