[analyzer][NFC] CallDescription should own the qualified name parts
Previously, CallDescription simply referred to the qualified name parts
by const char* pointers.
In the future we might want to dynamically load and populate
CallDescriptionMaps, hence we will need the CallDescriptions to
actually own their qualified name parts.
Reviewed By: martong, xazax.hun
Differential Revision: https://reviews.llvm.org/D113593