Fix #16500: look for interface files in -hidir flag in OneShot mode

We are currently ignoring options set in the hiDir field of hsc_dflags
when looking for interface files while compiling in OneShot mode. This
is inconsistent with the behaviour of other directory redirecting fields
(such as objectDir or hieDir). It is also inconsistent with the
behaviour of compilation in CompManager mode (a.k.a `ghc --make`) which
looks for interface files in the directory set in hidir flag. This
changes Finder.hs so that we use the value of hiDir while looking for
interface in OneShot mode.