Auto merge of #15539 - AdmiralCoco:reject_outofrange_transition_values, r=emilio

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] `./mach test-tidy` does not report any errors
- [X] These changes fix #15344

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- [X] There are tests for these changes

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