Auto merge of #145911 - notriddle:stringdex-tweak-3, r=GuillaumeGomez

rustdoc-search: yet another stringdex optimization attempt

This one's uses a different tactic. It shouldn't significantly increase the amount of downloaded index data, but still reduces the amount of disk usage.

This one works by changing the suffix-only node representation to omit some data that's needed for checking. Since those nodes make up the bulk of the tree, it reduces the data they store, but also requires validating the match by fetching the name itself (but the names list is pretty small, and when I tried it with wordnet "indexing" it was about the same).

r? `@GuillaumeGomez`