Rollup merge of #105796 - notriddle:notriddle/rustdoc-search-stop-doing-demerits...

Rollup merge of #105796 - notriddle:notriddle/rustdoc-search-stop-doing-demerits, r=GuillaumeGomez

rustdoc: simplify JS search routine by not messing with lev distance

Since the sorting function accounts for an `index` field, there's not much reason to also be applying changes to the levenshtein distance. Instead, we can just not treat `lev` as a filter if there's already a non-sentinel value for `index`.

<details>

This change gives slightly more weight to the index and path part, as search criteria, than it used to. This changes some of the test cases, but not in any obviously-"worse" way, and, in particular, substring matches are a bigger deal than levenshtein distances (we're assuming that a typo is less likely than someone just not typing the entire name).

The biggest change is the addition of a `path_lev` field to result items. It's always zero if the search query has no parent path part and for type queries, making the check in the `sortResults` function a no-op. When it's present, it is used to implement different precedence for the parent path and the tail.

Consider the query `hashset::insert`, a test case [that already exists and can be found here](https://github.com/rust-lang/rust/blob/5c6a1681a9a7b815febdd9de2f840da338984e68/src/test/rustdoc-js-std/path-ordering.js). We want the ordering shown in the test case:

```
        { 'path': 'std::collections::hash_set::HashSet', 'name': 'insert' },
        { 'path': 'std::collections::hash_set::HashSet', 'name': 'get_or_insert' },
        { 'path': 'std::collections::hash_set::HashSet', 'name': 'get_or_insert_with' },
        { 'path': 'std::collections::hash_set::HashSet', 'name': 'get_or_insert_owned' },
        { 'path': 'std::collections::hash_map::HashMap', 'name': 'insert' },
```

We do not want this ordering, which is the ordering that would occur if substring position took priority over `path_lev`:

```
        { 'path': 'std::collections::hash_set::HashSet', 'name': 'insert' },
        { 'path': 'std::collections::hash_map::HashMap', 'name': 'insert' }, // BAD
        { 'path': 'std::collections::hash_set::HashSet', 'name': 'get_or_insert' },
        { 'path': 'std::collections::hash_set::HashSet', 'name': 'get_or_insert_with' },
        { 'path': 'std::collections::hash_set::HashSet', 'name': 'get_or_insert_owned' },
```

We also do not want `HashSet::iter` to appear before `HashMap::insert`, which is what would happen if `path_lev` took priority over the appearance of any substring match. This is why the `sortResults` function has `path_lev` sandwiched between a `index < 0` check and a `index` comparison check:

```
        { 'path': 'std::collections::hash_set::HashSet', 'name': 'insert' },
        { 'path': 'std::collections::hash_set::HashSet', 'name': 'get_or_insert' },
        { 'path': 'std::collections::hash_set::HashSet', 'name': 'get_or_insert_with' },
        { 'path': 'std::collections::hash_set::HashSet', 'name': 'get_or_insert_owned' },
        { 'path': 'std::collections::hash_set::HashSet', 'name': 'iter' }, // BAD
        { 'path': 'std::collections::hash_map::HashMap', 'name': 'insert' },
```

The old code implemented a similar feature by manipulating the `lev` member based on whether a substring match was found and averaging in the path distance (`item.lev = name_lev + path_lev / 10`), so the path lev wound up acting like a tie breaker, but it gives slightly different results for `Vec::new`, [changing the test case](https://github.com/rust-lang/rust/pull/105796/files#diff-b346e2ef72a407915f438063c8c2c04f7a621df98923d441b41c0312211a5b21) because of the slight changes to ordering priority.

</details>

Based on https://github.com/rust-lang/rust/pull/103710#issuecomment-1296894296

Previews:

* https://notriddle.com/notriddle-rustdoc-demos/rustdoc-search-stop-doing-demerits/std/index.html
* https://notriddle.com/notriddle-rustdoc-demos/rustdoc-search-stop-doing-demerits-compiler/index.html