Add rejection of out-of-range values for single-timing-functions
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This PR fixes#15344, checking for the `cubic-bezier p1x/p2x` and `steps` first value after parsing.
There are unit tests that check for parsing of invalid values - I was not sure if there was a more suitable place, so I created a file (name subject to change).
Q: I found this [test suite](https://github.com/servo/servo/blob/master/tests/unit/style/properties/serialization.rs#L592), and noticed that the `p2x` value is out of range, but the test does not fail - is this because there is no check when calling the function itself?
Thanks!
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- [X] These changes fix#15344
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