Auto merge of #23758 - jdm:compositing-canvas-break, r=gterzian

Remove canvas->compositing dependency

There's one tiny place in the canvas crate that depends on the compositing crate, and it's really quite backwards. If we use trait objects instead it becomes much cleaner to reason about.

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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes do not require tests because no tests for windows-only webgl code.

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Cargo.lock

@@ -394,7 +394,6 @@ dependencies = [
  "azure 0.36.0 (git+https://github.com/servo/rust-azure)",
  "byteorder 1.2.7 (registry+https://github.com/rust-lang/crates.io-index)",
  "canvas_traits 0.0.1",
- "compositing 0.0.1",
  "cssparser 0.25.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "euclid 0.19.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "fnv 1.0.6 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -2542,6 +2541,7 @@ dependencies = [
  "msg 0.0.1",
  "net 0.0.1",
  "net_traits 0.0.1",
+ "offscreen_gl_context 0.22.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "profile 0.0.1",
  "profile_traits 0.0.1",
  "script 0.0.1",