rustdoc search: if all else is equal, rank alias results lower

[lolbinarycat]

a search for filter_map puts several methods not named filter_map before Iterator::filter_map.

[lolbinarycat]

This issue was discussed in this month's t-rustdoc meeting, along with #141475 and #140782.

The consensus was that this issue needs to be addressed either before those other issues, or simultaneously in the same PR.