Auto merge of #18592 - MortimerGoro:dom_texture, r=jdm

Implement DOM to texture

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This is a prototype of the WebGL DOMToTexture feature. The API should be fine as a privileged extension for now due to security concerns. The working group has been investigating the viability of unprivileged usage but the spec is not ready yet.

Demo video: https://www.youtube.com/watch?v=hpZqEM5hPao

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- [ ] These changes fix #__ (github issue number if applicable).

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Cargo.lock

@@ -311,6 +311,7 @@ dependencies = [
  "log 0.3.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "num-traits 0.1.37 (registry+https://github.com/rust-lang/crates.io-index)",
  "offscreen_gl_context 0.11.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "servo_config 0.0.1",
  "webrender 0.52.1 (git+https://github.com/servo/webrender)",
  "webrender_api 0.52.1 (git+https://github.com/servo/webrender)",
 ]