[clang] Exclude function pointers on DefaultedComparisonAnalyzer

This implements a more comprehensive fix than was done at D95409.
Instead of excluding just function pointer subobjects, we also
exclude any user-defined function pointer conversion operators.

Signed-off-by: Matheus Izvekov <mizvekov@gmail.com>

Reviewed By: rsmith

Differential Revision: https://reviews.llvm.org/D103855