[Reduce] Basic block reduction: do properly handle invoke insts (PR46818)

Terminator may have returned value, so we need to replace uses,
and in general handle invoke as a branch inst.

I'm not sure this is the best handling, but IMO poorly reduced
input is much better than crashing reduction tool.
A (previously-crashing!) test added.

Fixes https://bugs.llvm.org/show_bug.cgi?id=46818