Optional backtraces for JS errors and WebGL errors
This adds two new build-time features to enable useful debugging tools when investigating why JS and WebGL content isn't working. They're optional because they're quite heavyweight.
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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 do not require tests because they're optional developer features.
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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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The expectation change is due to the shader now using its DOM-side compile status.
It is actually a bug for the shader to think it actually compiled successfully,
but at least it does so consistently now.
Respect the source rectangle when drawing a canvas to another canvas.
This allows us to run the three.js examples without panicking, since they use self-drawing canvases to scroll the FPS graph.
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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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