Kernel: Fix some issues related to fixes and block conditions

Fix some problems with join blocks where the joining thread block
condition was added twice, which lead to a crash when trying to
unblock that condition a second time.

Deferred block condition evaluation by File objects were also not
properly keeping the File object alive, which lead to some random
crashes and corruption problems.

Other problems were caused by the fact that the Queued state didn't
handle signals/interruptions consistently. To solve these issues we
remove this state entirely, along with Thread::wait_on and change
the WaitQueue into a BlockCondition instead.

Also, deliver signals even if there isn't going to be a context switch
to another thread.

Fixes #4336 and #4330

Kernel/FileSystem/FIFO.cpp

@@ -71,7 +71,7 @@ NonnullRefPtr<FileDescription> FIFO::open_direction_blocking(FIFO::Direction dir
 
         if (m_writers == 0) {
             locker.unlock();
-            Thread::current()->wait_on(m_write_open_queue, "FIFO");
+            m_write_open_queue.wait_on(nullptr, "FIFO");
             locker.lock();
         }
     }
@@ -81,7 +81,7 @@ NonnullRefPtr<FileDescription> FIFO::open_direction_blocking(FIFO::Direction dir
 
         if (m_readers == 0) {
             locker.unlock();
-            Thread::current()->wait_on(m_read_open_queue, "FIFO");
+            m_read_open_queue.wait_on(nullptr, "FIFO");
             locker.lock();
         }
     }

Kernel/FileSystem/File.h

@@ -142,17 +142,24 @@ protected:
     {
         if (Processor::current().in_irq()) {
             // If called from an IRQ handler we need to delay evaluation
-            // and unblocking of waiting threads
-            Processor::deferred_call_queue([this]() {
-                ASSERT(!Processor::current().in_irq());
-                evaluate_block_conditions();
+            // and unblocking of waiting threads. Note that this File
+            // instance may be deleted until the deferred call is executed!
+            Processor::deferred_call_queue([self = make_weak_ptr()]() {
+                if (auto file = self.strong_ref())
+                    file->do_evaluate_block_conditions();
             });
         } else {
-            block_condition().unblock();
+            do_evaluate_block_conditions();
         }
     }
 
 private:
+    ALWAYS_INLINE void do_evaluate_block_conditions()
+    {
+        ASSERT(!Processor::current().in_irq());
+        block_condition().unblock();
+    }
+
     FileBlockCondition m_block_condition;
 };