Fix radial gradient's <size>/<ending-shape> parsing
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Parsing now handles sizes and shapes in various order.
I had to delete `EndingShape`'s parse implementation and mix it with `Position` in `parse_radial`. It became a bit complicated to read but I couldn't make it simpler.
r? @Manishearth
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style: Don't incorrectly clamp values in calc that might not be only lengths.
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Expressions with percentages may be negative or positive at computed value time.
So, we can only clamp lengths at computed value time, which is what the other
browsers do.
Handle specialized serialization of <position> in basic shapes
Fixes#13083
We temporarily broke basic-shape serialization in #13042 when 4-value positions were implemented, since I didn't want to increase the scope of that PR too much.
This fixes it.
r? @SimonSapin
cc @canaltinova
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Prefer length and percentage for word spacing
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The goal is to make use of `LengthOrPercentage` for word spacing in `ShapingOptions`, but since it makes use of `f32` which doesn't implement `Hash`, we're going for `NotNan<f32>` from [ordered-float](https://github.com/reem/rust-ordered-float/), which supports hashing. Instead of implementing `Hash` for `LengthOrPercentage` and thereby the inner types like `CSSFloat`, `CalcLengthOrPercentage`, etc., we convert it to `(Au, NotNan<f32>)`.
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