Various webgl fixes for framebuffer attachment test
These changes resolve all panics on macOS when running framebuffer-object-attachment.html in headless and headful testing.
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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] There are tests for these changes OR
- [x] Fixes#13710. Fixes#20570.
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Reacting to environment changes
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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix a subset of #11416
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- [x] These changes do not require tests because they will be added when the complete responsive images is complete
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Enable wasm tests.
Now that we support WASM, we should avoid regressing that existing support and get a better idea about the pieces we're still missing.
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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] There are tests for these changes
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correct currentSrc function
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(recreating PR which got closed earlier https://github.com/servo/servo/pull/21521)
<!-- 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).
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- [x] There are tests for these changes
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