[analyzer][NFC][MallocChecker] Convert many parameters into CallEvent

Exactly what it says on the tin! This is clearly not the end of the road in this
direction, the parameters could be merged far more with the use of CallEvent or
a better value type in the CallDescriptionMap, but this was shockingly difficult
enough on its own. I expect that simplifying the file further will be far easier
moving forward.

The end goal is to research how we could create a more mature checker
interaction infrastructure for more complicated C++ modeling, and I'm pretty
sure that being able successfully split up our giants is the first step in this
direction.

Differential Revision: https://reviews.llvm.org/D75432