Kernel: Rewrite ThreadBlocker

This gets rid of a very old bug where kernel panics when thread is being
woken up and unblocked at the same time on different cores. This
required adding a new lock to SchedulerQueue::Node and adding a cap to
how many threads a threadblocker can simultaneously block. I don't think
I ever block more than five threads on the same ThreadBlocker so this
should be fine.

kernel/include/kernel/Scheduler.h

@@ -14,33 +14,12 @@ namespace Kernel
 	class BaseMutex;
 	class Thread;
 	class ThreadBlocker;
+	struct SchedulerQueueNode;
 
 	class SchedulerQueue
 	{
 	public:
-		struct Node
-		{
-			Node(Thread* thread)
-				: thread(thread)
-			{}
-
-			Thread* const thread;
-
-			Node* next { nullptr };
-			Node* prev { nullptr };
-
-			uint64_t wake_time_ns { static_cast<uint64_t>(-1) };
-
-			ThreadBlocker* blocker { nullptr };
-			Node* block_chain_next { nullptr };
-			Node* block_chain_prev { nullptr };
-
-			ProcessorID processor_id { PROCESSOR_NONE };
-			bool blocked { false };
-
-			uint64_t last_start_ns { 0 };
-			uint64_t time_used_ns  { 0 };
-		};
+		using Node = SchedulerQueueNode;
 
 	public:
 		void add_thread_to_back(Node*);