Rollup merge of #90727 - GuillaumeGomez:remove-potential-useless-search-index-data...

Rollup merge of #90727 - GuillaumeGomez:remove-potential-useless-search-index-data, r=notriddle,camelid

Remove potential useless data for search index

I uncovered this case when working on https://github.com/rust-lang/rust/pull/90726 to debug https://github.com/rust-lang/rust/pull/90385.

Explanations: if we have a full generic, we check if it has generics then we do the following:
 * If it has only one generic, we remove one nested level in order to not keep the "parent" generic (since it has empty name, it's useless after all).
 * Otherwise we add it alongside its generics.

However, I didn't handle the case where a generic had no generics. Meaning that we were adding items with empty names in the search index. So basically useless data in the search index.

r? `@camelid`