Auto merge of #14471 - heycam:blockification, r=emilio

adjust display style fixup to handle more Gecko cases

<!-- Please describe your changes on the following line: -->

This tweaks the display property fixup we do when restyling to:

* handle the display values that Gecko supports that Servo doesn't
* blockify grid items (like we do flex items)
* skip the fixup for NAC

And while I'm in the area, this sets `nsStyleDisplay::mOriginalDisplay` too.

r? @bholley cc @SimonSapin

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

<!-- Either: -->
- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because _____

<!-- 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/14471)
<!-- Reviewable:end -->

0 files changed, 0 insertions, 0 deletions