aconfig: change flag values to enabled/disabled enum

Change the underlying type of a flag's value from bool to an explicit
enum (Disabled, Enabled): this will hopefully reduce future confusion on
how flags are intended to be used.

Bug: 279485059
Test: atest aconfig.test
Change-Id: I9535f9b23baf93ad5916ca06fb7d21277b4573eb
diff --git a/tools/aconfig/protos/aconfig.proto b/tools/aconfig/protos/aconfig.proto
index d95fd50..6eac414 100644
--- a/tools/aconfig/protos/aconfig.proto
+++ b/tools/aconfig/protos/aconfig.proto
@@ -20,13 +20,18 @@
 
 package android.aconfig;
 
+enum flag_state {
+  ENABLED = 1;
+  DISABLED = 2;
+}
+
 enum permission {
   READ_ONLY = 1;
   READ_WRITE = 2;
 }
 
 message value {
-  required bool value = 1;
+  required flag_state state = 1;
   required permission permission = 2;
   optional uint32 since = 3;
 }
@@ -43,7 +48,7 @@
 
 message override {
   required string id = 1;
-  required bool value = 2;
+  required flag_state state = 2;
   required permission permission = 3;
 };