Update parse_length to match spec
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There are a few canvas2d-related dependencies that haven't updated, but they
only use euclid internally so that's not blocking landing the rest of the
changes.
Given the size of this patch, I think it's useful to get this landed as-is.
Clipboard refactoring
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This PR removes clipboard handling from the constellation. Instead, now embedder handles it.
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ISSUE-20455: introduce stronger types for textinput indexing
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Added two new types:
- ByteOffset
- UTF16CodeUnitOffset
I've replaced any instance of `usize` that would be better represented by one or the other of these. I also updated any downstream code, including the unit tests for `textinput.rs`. Along the way, I tried to add or edit comments to better reflect my understanding of this file - happy to revisit if I have misrepresented anything.
I did not end up finding any places where types were very obviously being mixed, as the issue description suggested I should do... LMK if I should re-audit the file for that (might need a bit of guidance)!
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This includes a `size_of` regression for a few DOM types,
due to https://github.com/rust-lang/rust/pull/58623 which replaces the
implementation of `HashMap` in the standard library to Hashbrown.
Although `size_of<HashMap>` grows, it’s not obvious how total memory usage
is going to be impacted: Hashbrown only has one `u8` instead of one `usize`
of overhead per hash table bucket for storing (part of) a hash,
and so might allocate less memory itself.
Hashbrown also typically has better run time performance:
https://github.com/rust-lang/hashbrown#performance
Still, I’ve filed https://github.com/rust-lang/hashbrown/issues/69
about potentially reducing the `size_of<HashMap>` regression.
