Require 'exact', 'prefix', or '' for match operation in property_contexts

The previous code would lazily check for 'exact' and accept any other
value as a prefix match.  This should be a tighter check allowing only
'exact', 'prefix', or an empty string for this option.

Test: build fails if an invalid string is used for the match operation
Test: build succeeds normally
Test: `getprop -Z` shows exact vs prefix is differentiated correctly
Change-Id: I21dcb193810d65f468f8960967eabfd261f71e21
diff --git a/init/property_service.cpp b/init/property_service.cpp
index adf8929..5b35ad2 100644
--- a/init/property_service.cpp
+++ b/init/property_service.cpp
@@ -925,7 +925,8 @@
     }
 
     auto errors = std::vector<std::string>{};
-    ParsePropertyInfoFile(file_contents, property_infos, &errors);
+    bool require_prefix_or_exact = SelinuxGetVendorAndroidVersion() >= __ANDROID_API_R__;
+    ParsePropertyInfoFile(file_contents, require_prefix_or_exact, property_infos, &errors);
     // Individual parsing errors are reported but do not cause a failed boot, which is what
     // returning false would do here.
     for (const auto& error : errors) {