This lets us generate long lists of settings permutations by writing a
simple JSON spec. For example, the following spec would generate six
`Settings` objects, all of which have SSAO enabled. See the unit test
for a larger example.
```
{
"name": "viewopts",
"base": { "view.ssao.enabled": true }
"permute": {
"view.dithering": ["NONE", "TEMPORAL"],
"view.sampleCount": [1, 4, 8]
}
}
```
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