framework/util: optimize get_rpm_nvr_by_type by adding a cache
    
    The cache build could be optimized by assuming that all modules with
    priority 100 are part of selinux-policy-<policytype> package. This way
    the cache would only have to contain types from modules of other
    priorities.
    
    Another optimization would be making the cache persistent. This way it
    would only have to be rebuild on policy reload (sedispatch could trigger
    cache rebuild over dbus).
    
    My testing shows significant time save when processing multiple AVCs:
    setroubleshoot-server-3.3.24-1.el8:
    real	2m26.075s
    user	2m17.989s
    sys	0m5.916s
    
    Cache:
    real	0m15.337s
    user	0m11.004s
    sys	0m3.995s
    
    But curiously, there is also a small time save for individual AVCs
    (measured by forcing the cache rebuild for each call of
    get_rpm_nvr_by_type):
    real	1m40.393s
    user	1m32.830s
    sys	0m5.960s
    
    It could be caused by processing policy modules by lines, which quickly
    eliminates all lines not starting by "(type " (as opposed to comparing
    the regular expression with the whole file).