Fix/suppress system/security google-explicit-constructor warnings

* Add explicit to conversion constructors/operators
* Use NOLINT or NOLINTNEXTLINE to suppress warnings on intended converters

Bug: 28341362
Test: make with WITH_TIDY=1 DEFAULT_GLOBAL_TIDY_CHECKS=-*,google-explicit-constructor
Change-Id: I4ed5aea36fcdcd8dbda9a4be9607c5af606f2a08
diff --git a/keystore/grant_store.h b/keystore/grant_store.h
index f8e4f91..1baf32c 100644
--- a/keystore/grant_store.h
+++ b/keystore/grant_store.h
@@ -48,6 +48,7 @@
 
   uint64_t grant_no_;  ///< numeric grant identifier - randomly assigned
 
+  // NOLINTNEXTLINE(google-explicit-constructor)
   operator const uint64_t&() const { return grant_no_; }
 };