CApiFFI: add ConstPtr for encoding const-qualified pointer return types (#22043)
Previously, when using capi
calling convention in foreign declarations,
code generator failed to handle const-cualified pointer return types.
This resulted in CC toolchain throwing -Wincompatible-pointer-types-discards-qualifiers
warning.
Foreign.C.Types.ConstPtr
newtype was introduced to handle these cases -
special treatment was put in place to generate appropritetly qualified C
wrapper that no longer triggers the above mentioned warning.
Fixes #22043 (closed)