webxr: Implement MallocSizeOf (#42505)

Implement MallocSizeOf for most of WebXr. Mostly uncontroversal changes.
Of note:
- Implementation of size_of for euclid::RigidTransform
- Implementation of size_of for euclid::Vector3D
- Join is currently ignored as the type is very complicated.

Signed-off-by: Narfinger <Narfinger@users.noreply.github.com>

*Describe the changes that this pull request makes here. This will be
the commit message.*

Testing: Compilation is the test.

Signed-off-by: Narfinger <Narfinger@users.noreply.github.com>

components/script/dom/webgpu/gpucommandbuffer.rs

@@ -14,7 +14,6 @@ use crate::dom::globalscope::GlobalScope;
 use crate::script_runtime::CanGc;
 #[derive(JSTraceable, MallocSizeOf)]
 struct DroppableGPUCommandBuffer {
-    #[ignore_malloc_size_of = "defined in webgpu"]
     #[no_trace]
     channel: WebGPU,
     #[no_trace]