Issue #20593: Implement proper checks in WebGLRenderingContext's getFramebufferAttachmentParameter().
Add missing input checks.
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- [X] `./mach build -d` does not report any errors
- [X] `./mach build-geckolib` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix#20593
- [X] There are tests for these changes
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