rta: add `live_types_to_csv` to provide human-readable info on types

Signed-off-by: Jean Privat <jean@pryen.org>
rta: add `live_methods_to_tree` to provide human-readable infos on methods

Signed-off-by: Jean Privat <jean@pryen.org>
metrics/rta: save the list of live things in files

Simply use `live_types_to_csv` and `live_methods_to_tree` to produce
two files in the correct output directory.

This helps the debugging of engines when RTA is buggy or misused.

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