Kernel: Add bitwise operators for Thread::FileBlocker::BlockFlags enum

Switch to using type-safe bitwise operators for the BlockFlags class,
this cleans up a lot of boilerplate casts which are necessary when the
enum is declared as `enum class`.

Kernel/Thread.h

@@ -26,6 +26,7 @@
 
 #pragma once
 
+#include <AK/EnumBits.h>
 #include <AK/Function.h>
 #include <AK/HashMap.h>
 #include <AK/IntrusiveList.h>
@@ -1267,6 +1268,8 @@ private:
     void drop_thread_count(bool);
 };
 
+AK_ENUM_BITWISE_OPERATORS(Thread::FileBlocker::BlockFlags);
+
 template<typename Callback>
 inline IterationDecision Thread::for_each(Callback callback)
 {