servo: Merge #12783 - Prefer length and percentage for word spacing (from Wafflespeanut:word_spacing); r=Manishearth

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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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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors

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- [ ] There are tests for these changes

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Source-Repo: https://github.com/servo/servo
Source-Revision: 3b676bc85dc66ed0e80756204f347bf1842b01a0

servo/python/tidy/servo_tidy/tidy.py

@@ -261,7 +261,7 @@ def check_lock(file_name, contents):
         raise StopIteration
 
     # package names to be neglected (as named by cargo)
-    exceptions = ["lazy_static"]
+    exceptions = ["lazy_static", "unreachable", "void"]
 
     import toml
     content = toml.loads(contents)