Auto merge of #17436 - bradwerth:updateStylesheet, r=xidorn,emilio

Add an update_stylesheet method to StylesheetSet.

MozReview-Commit-ID: KlRkApYL8wk

<!-- Please describe your changes on the following line: -->
Provides a method for just-cloned sheets to be swapped in to stylesheet_sets without changing the order or triggering restyle.

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

<!-- 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/17436)
<!-- Reviewable:end -->

components/style/gecko/generated/bindings.rs

@@ -1885,6 +1885,11 @@ extern "C" {
                                                  unique_id: u64,
                                                  before_unique_id: u64);
 }
+extern "C" {
+    pub fn Servo_StyleSet_UpdateStyleSheet(set: RawServoStyleSetBorrowed,
+                                           sheet: RawServoStyleSheetBorrowed,
+                                           unique_id: u64);
+}
 extern "C" {
     pub fn Servo_StyleSet_FlushStyleSheets(set: RawServoStyleSetBorrowed,
                                            doc_elem: