Add option to print mangled function names

To compare vtable in VTS ABI test, add the option -mangled to have
vndk-vtable-dumper print mangled function names. If the option is not
specified, print demangled names.

Bug: 37488823
Test: tests/test_vndk_vtable_dumper.py
Test: vndk-vtable-dumper -mangled libhidlbase.so
Change-Id: I0a57089425298d311e2366adb933c4c752a37b03