This includes a `size_of` regression for a few DOM types,
due to rust-lang/rust#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 rust-lang/hashbrown#69
about potentially reducing the `size_of<HashMap>` regression.