LibJS: Always inline HeapBlock::allocate()

This thing is so simple and sits on the hot path so just inline it.

Libraries/LibJS/Heap/HeapBlock.cpp

@@ -73,13 +73,6 @@ HeapBlock::HeapBlock(Heap& heap, size_t cell_size)
     m_freelist = next;
 }
 
-Cell* HeapBlock::allocate()
-{
-    if (!m_freelist)
-        return nullptr;
-    return exchange(m_freelist, m_freelist->next);
-}
-
 void HeapBlock::deallocate(Cell* cell)
 {
     ASSERT(cell->is_live());

Libraries/LibJS/Heap/HeapBlock.h

@@ -42,7 +42,13 @@ public:
     size_t cell_size() const { return m_cell_size; }
     size_t cell_count() const { return (block_size - sizeof(HeapBlock)) / m_cell_size; }
 
-    Cell* allocate();
+    ALWAYS_INLINE Cell* allocate()
+    {
+        if (!m_freelist)
+            return nullptr;
+        return exchange(m_freelist, m_freelist->next);
+    }
+
     void deallocate(Cell*);
 
     template<typename Callback>