Auto merge of #19755 - streichgeorg:decoupling_metrics_gfx, r=jdm

Decouple metrics and gfx

Added gfx_traits::DisplayList so metrics doesn't depend on the gfx crate for gfx::display_list::DisplayList.

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #19422 (github issue number if applicable).

<!-- Either: -->
- [ ] There are tests for these changes OR
- [X] These changes do not require tests because succesful compilation should be enough

<!-- Also, please make sure that "Allow edits from maintainers" checkbox is checked, so that we can help you if you get stuck somewhere along the way.-->

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/19755)
<!-- Reviewable:end -->

Cargo.lock

@@ -1762,7 +1762,6 @@ dependencies = [
 name = "metrics"
 version = "0.0.1"
 dependencies = [
- "gfx 0.0.1",
  "gfx_traits 0.0.1",
  "ipc-channel 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.3.8 (registry+https://github.com/rust-lang/crates.io-index)",