This change is the residue of a failed attempt to reduce the scope
of the Implementations query (and others) based on a misunderstanding.
It merely improves the documentation around these two concepts.
What is the German word for a lengthy effort that ends in
nothing more than a small amount of wistful documentation?

Also, return errors correctly in InlayHint, which I touched along
the way.

Change-Id: I5023d0abffed8d0d9cfd8a18668ba859e8fabbc2
Reviewed-on: https://go-review.googlesource.com/c/tools/+/493625
Run-TryBot: Alan Donovan <[email protected]>
Reviewed-by: Robert Findley <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>