Move the part of compile_rule_infos that actually compiled a condition
string into a sinsp_filter into a standalone method
compile_condition(). That way it can be used by classes that derive
from rule_loader::compiler() and want to compile condition strings.
This implementation also saves the compiled filter as a part of the
falco_rule object so it does not need to be compiled again wihin the
falco engine after rules loading.
Signed-off-by: Mark Stemm <mark.stemm@gmail.com>