We currently handle this by RAV-visiting OverloadExprs and basically
picking the first decl in the candidate set.
To make this more rigorous, I guess we would have to use the arguments
from the originating CallExpr to find the best match. Is there library
support in e.g. Sema to do this? Since IWYU assumes working code, we
know there's exactly one candidate that will be selected, we just need
to be able to resolve which one. I'm looking for something like: