Split Call into Call and DivergingCall

Split Call into Call and DivergingCall

DivergingCall is different enough from the regular converging Call to warrant the split. This also
inlines CallData struct and creates a new CallTargets enum in order to have a way to differentiate
between calls that do not have an associated cleanup block.

Note, that this patch still does not produce DivergingCall terminator anywhere. Look for that in
the next patches.