Auto merge of #12243 - TravisDean:else-brace-check, r=ConnorGBrewster

Add style check and test for else braces

<!-- 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).

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

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components/compositing/compositor.rs

@@ -2261,8 +2261,7 @@ impl<Window: WindowMethods> IOCompositor<Window> {
                             rendergl::render_scene(layer.clone(), context, &self.scene);
                             gl::disable(gl::SCISSOR_TEST);
 
-                        }
-                        else {
+                        } else {
                             rendergl::render_scene(layer.clone(), context, &self.scene);
                         }
                     }