Verify the SELabels used in property_contexts

Verify that the SELabels used in property_contexts correspond to a
real type in the SEPolicy and that this type has the property_type attribute.

Additionally add a check that vendor property_context files do not
duplicate entries in plat property_contexts, and a similar check that
odm property_contexts doesn't duplicate either plat or vendor
property_contexts.

Bug: 74078792
Test: Build property_contexts on bullhead successfully
Test: See failure when using a faulty SELabel in property_contexts
Test: See failure when duplicating label in vendor and plat property_contexts
Change-Id: I4d2338dab68f1c5a8ed110aa7821f0677f61bafb