[analyzer] Dump checker name if multiple checkers evaluate the same call

Previously, if accidentally multiple checkers `eval::Call`-ed the same
`CallEvent`, in debug builds the analyzer detected this and crashed
with the message stating this. Unfortunately, the message did not state
the offending checkers violating this invariant.
This revision addresses this by printing a more descriptive message
before aborting.

Reviewed By: martong

Differential Revision: https://reviews.llvm.org/D112889