[-Wunsafe-buffer-usage] Group parameter fix-its

For a function `F` whose parameters need to be fixed, we group fix-its
of F's parameters together so that either all of the parameters get
fixed or none of them gets fixed.

Reviewed by: NoQ (Artem Dergachev), t-rasmud (Rashmi Mudduluru), jkorous (Jan Korous)

Differential revision: https://reviews.llvm.org/D153059