Optimize findRef
Optimize findRef

Use simple test firsts in Import#selection (where not finding
something is the norm), and avoid re-selection of `ctx.owner`.

lampepfl/dotty,lampepfl/dotty,dotty-staging/dotty,lampepfl/dotty,dotty-staging/dotty,sjrd/dotty,dotty-staging/dotty,dotty-staging/dotty,sjrd/dotty,sjrd/dotty,lampepfl/dotty,sjrd/dotty,lampepfl/dotty,sjrd/dotty,dotty-staging/dotty