rustdoc: search for type alias says "type X not found, showing type X instead"

[CAD97]

The "In Names" search tab is fine, but the "In Parameters" and "In Return Types" have the confusing note that e.g.

Type "pid_t" not found. Showing results for closest type name "pid_t" instead.

@rustbot label: +T-rustdoc +A-rustdoc-ui