nitg-s: do not compile_class_to_c for abstract classes and interfaces

Signed-off-by: Jean Privat <jean@pryen.org>
rta: add RapidTypeAnalysis::live_classes

Signed-off-by: Jean Privat <jean@pryen.org>
nitg-s: compile_class_to_c works less for dead classes

Signed-off-by: Jean Privat <jean@pryen.org>
phases: stop displaying location for property on verbose level 4

Signed-off-by: Jean Privat <jean@pryen.org>
model: cache `to_s` for MClassDef, MGenericType, MNullableType, MPropDef

Signed-off-by: Jean Privat <jean@pryen.org>