Add VTTRegion and part of VTTCue DOM interfaces
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Hello! In this PR I implemented the VTTRegion DOM interface and part of VTTCue (#22312). Before continuing I thought it's maybe a good idea to first request a review or even merge what I did up to this point, as I might get stuck on the next part. I have a slight idea of what needs to be done (I assume it's hooking the GStreamer parser somewhere in `GetCueAsHTML()`), but a short outline or some more instructions would help a lot.
I updated test expectations by first running:
```
./mach test-wpt tests/wpt/web-platform-tests/webvtt/api --log-raw servo.log --pref dom.webvtt.enabled=true
```
then
```
./mach update-wpt servo.log
```
Thanks!
---
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Add new Servo Logo
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* Added servo-64.png (replacing servo64.png @ 64px)
* Added servo-100.png (replacing doge-tiny.png @ 100px)
* Added servo-500.png
* Added servo-500-icon.ico
* Added servo-1000.png (replacing servo.png @ 1000px)
* Added servo.svg (replacing servo.svg)
---
<!-- 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
- [ ] These changes fix #___ (GitHub issue number if applicable)
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- [ ] There are tests for these changes OR
- [X] These changes do not require tests because they add new logo assets
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