servo: Merge #16940 - upload geckolib docs to doc.servo.org (from ccarruitero:fix16887); r=emilio

<!-- Please describe your changes on the following line: -->
add `geckolib` docs into upload docs script

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [ ] `./mach build -d` does not report any errors
- [ ] `./mach test-tidy` does not report any errors
- [X] These changes fix #16887

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- [ ] There are tests for these changes OR
- [X] These changes do not require tests because are in ci script

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Source-Repo: https://github.com/servo/servo
Source-Revision: 166abb82bc1ab56343002d8acd365c5d20795ba0

--HG--
extra : subtree_source : https%3A//hg.mozilla.org/projects/converted-servo-linear
extra : subtree_revision : 1974b178c1702367b804595142d4de50d7e4bf44

servo/etc/ci/upload_docs.sh

@@ -18,6 +18,10 @@ cd "$(dirname ${0})/../.."
 # etc/doc.servo.org/index.html overwrites $(mach rust-root)/doc/index.html
 cp etc/doc.servo.org/* target/doc/
 
+./mach cargo-geckolib doc
+mkdir target/doc/geckolib
+cp target/geckolib/doc/* target/doc/geckolib/
+
 python components/style/properties/build.py servo html regular
 
 cd components/script