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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build(deps): bump openssl from 0.10.29 to 0.10.30
Bumps [openssl](https://github.com/sfackler/rust-openssl) from 0.10.29 to 0.10.30.
<details>
<summary>Commits</summary>
<ul>
<li><a href="d8395ba415"><code>d8395ba</code></a> Release openssl v0.10.30</li>
<li><a href="ff4a2152dc"><code>ff4a215</code></a> Merge pull request <a href="https://github-redirect.dependabot.com/sfackler/rust-openssl/issues/1306">#1306</a> from crdumoul/master</li>
<li><a href="78c77b288c"><code>78c77b2</code></a> Add SslStream::from_raw_parts</li>
<li><a href="164bb84bd1"><code>164bb84</code></a> Merge pull request <a href="https://github-redirect.dependabot.com/sfackler/rust-openssl/issues/1299">#1299</a> from flokli/siganture</li>
<li><a href="3e12906302"><code>3e12906</code></a> sign.rs: fix typo in comment</li>
<li><a href="2f98f1c821"><code>2f98f1c</code></a> Fix CI branch</li>
<li><a href="f5c89a0b94"><code>f5c89a0</code></a> remove appveyor builds</li>
<li><a href="7546bfd148"><code>7546bfd</code></a> Ignore default verify paths test on windows</li>
<li><a href="60118dddad"><code>60118dd</code></a> test env lookup</li>
<li><a href="52c1b6fdc2"><code>52c1b6f</code></a> set vcpkg root</li>
<li>Additional commits viewable in <a href="https://github.com/sfackler/rust-openssl/compare/openssl-v0.10.29...openssl-v0.10.30">compare view</a></li>
</ul>
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