rustdoc search: for argument based searches, deprioritize associated items

[lolbinarycat]

Inspired by discussion on #131806, opening an issue so it can be discussed separately.

currently, both "In Parameters" and "Type ->" searches are dominated by methods on that type (and if the aforementioned PR is merged, fields will also clutter such searches)

however, associated items for a type can easily be viewed simply by going to that type's page, so arguably this form of search should prioritize free functions and methods of other types, which are harder to find.

this could be considered the dual of #134935

[notriddle]

When you say, "associated items for a type," do you specifically mean items that are associated with the item that you're searching for?

[lolbinarycat]

yes.