Auto merge of #153799 - notriddle:stringdex-0.0.6, r=GuillaumeGomez

rustdoc-search: update to stringdex 0.0.6

This update includes a few optimizations that reduce the size and index building time:

- the wire format uses two bits to store four possibilities, instead of only handling three https://gitlab.com/notriddle/stringdex/-/merge_requests/34

- the hashes themselves are 40 bits instead of 48, and inlining is able to still fit enough data by storing runs https://gitlab.com/notriddle/stringdex/-/merge_requests/35

- scanning for duplicates takes advantage of the rarity of conflicts, using an array with 32 bit numbers and only pulling in the other 8 bits when actually needed https://gitlab.com/notriddle/stringdex/-/merge_requests/37

Author: bors