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.