Change a lookupCtxt to lookupCtxtExact
Change a lookupCtxt to lookupCtxtExact

Except when disambiguating, we should always use the latter to look up
resolved names. Otherwise, we get surprising ambiguity errors where
there is no ambiguity, or similarly odd behaviour.

Fixes #3625

Heather/Idris-dev,FranklinChen/Idris-dev,FranklinChen/Idris-dev,uuhan/Idris-dev,Heather/Idris-dev,Heather/Idris-dev,kojiromike/Idris-dev,jmitchell/Idris-dev,FranklinChen/Idris-dev,mpkh/Idris-dev,markuspf/Idris-dev,FranklinChen/Idris-dev,uuhan/Idris-dev,kojiromike/Idris-dev,kojiromike/Idris-dev,uuhan/Idris-dev,mpkh/Idris-dev,markuspf/Idris-dev,jmitchell/Idris-dev,Heather/Idris-dev,jmitchell/Idris-dev,Heather/Idris-dev,kojiromike/Idris-dev,uuhan/Idris-dev,markuspf/Idris-dev,jmitchell/Idris-dev,uuhan/Idris-dev,mpkh/Idris-dev,markuspf/Idris-dev,FranklinChen/Idris-dev,mpkh/Idris-dev,uuhan/Idris-dev,uuhan/Idris-dev,markuspf/Idris-dev,kojiromike/Idris-dev,markuspf/Idris-dev,jmitchell/Idris-dev,Heather/Idris-dev,jmitchell/Idris-dev,markuspf/Idris-dev,mpkh/Idris-dev,kojiromike/Idris-dev,mpkh/Idris-dev,FranklinChen/Idris-dev