<!-- Please describe your changes on the following line: -->
Added a regex check to enforce project style guidelines. Added unit check. Catches:
```
}
else {
```
when it should be
`} else {`
---
<!-- 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 (no core files changed)
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix#12234 (github issue number if applicable).
<!-- Either: -->
- [X] There are tests for these changes OR
- [ ] These changes do not require tests because _____
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Source-Repo: https://github.com/servo/servo
Source-Revision: e21b47c2cc14897380a8c4ef2dfa650b1dd48ab5
6324c89567