Make hiddenAPIFlagFileCategory an int

hiddenAPIFlagFileCategory used to contain function pointers, and is
used in a provider. Providers must be serializable for incremental
soong support, so the function pointers must be removed.

Refactor hiddenAPIFlagFileCategory into a simple int.

Bug: 322069292
Test: m nothing --no-skip-soong-tests
Change-Id: I2bd50fa1b59979f30869b405314cbef16ee345f1
diff --git a/java/bootclasspath_fragment_test.go b/java/bootclasspath_fragment_test.go
index 95cd4a9..8bc0a7e 100644
--- a/java/bootclasspath_fragment_test.go
+++ b/java/bootclasspath_fragment_test.go
@@ -467,10 +467,10 @@
 	android.AssertArrayString(t, "single packages", []string{"newlibrary.mine"}, info.SinglePackages)
 	for _, c := range HiddenAPIFlagFileCategories {
 		expectedMaxTargetQPaths := []string(nil)
-		if c.PropertyName == "max_target_q" {
+		if c.PropertyName() == "max_target_q" {
 			expectedMaxTargetQPaths = []string{"my-new-max-target-q.txt"}
 		}
-		android.AssertPathsRelativeToTopEquals(t, c.PropertyName, expectedMaxTargetQPaths, info.FlagFilesByCategory[c])
+		android.AssertPathsRelativeToTopEquals(t, c.PropertyName(), expectedMaxTargetQPaths, info.FlagFilesByCategory[c])
 	}
 
 	// Make sure that the signature-patterns.csv is passed all the appropriate package properties