Auto merge of #100150 - notriddle:notriddle/implementors-js, r=GuillaumeGomez

rustdoc: use a more compact encoding for implementors/trait.*.js

The exact amount that this reduces the size of an implementors file depends on whether most of the impls are synthetic or not. For `Send`, it reduces the file from 128K to 112K, while for `Clone` it went from 64K to 44K.

Author: bors