Rollup merge of #143988 - GuillaumeGomez:alias-inexact, r=lolbinarycat

[rustdoc] Make aliases search support partial matching

Fixes rust-lang/rust#140782.

To make this work, I moved aliases into the `searchIndex` like any other item. It links to the "original" item with a new `original` field. No so great part is that we need to have some fields like `bitIndex` to be set on the alias to make the description load to work but I consider it minor enough to be ok.

This PR voluntarily doesn't handle de-prioritization of aliases as ```@lolbinarycat``` wished to work on this so I'll leave them this part. 😉

cc ```@lolbinarycat```

Author: matthiaskrgr