Revert "Replace LowLevelLock with Lock (#94991)"

This reverts commit 3b61ad9.

src/coreclr/nativeaot/System.Private.CoreLib/src/Internal/Runtime/FrozenObjectHeapManager.cs

@@ -16,7 +16,7 @@ internal unsafe partial class FrozenObjectHeapManager
     {
         public static readonly FrozenObjectHeapManager Instance = new FrozenObjectHeapManager();
 
-        private readonly Lock m_Crst = new Lock();
+        private readonly LowLevelLock m_Crst = new LowLevelLock();
         private FrozenObjectSegment m_CurrentSegment;
 
         // Default size to reserve for a frozen segment
@@ -34,7 +34,9 @@ internal unsafe partial class FrozenObjectHeapManager
         {
             HalfBakedObject* obj = null;
 
-            using (m_Crst.EnterScope())
+            m_Crst.Acquire();
+
+            try
             {
                 Debug.Assert(type != null);
                 // _ASSERT(FOH_COMMIT_SIZE >= MIN_OBJECT_SIZE);
@@ -82,6 +84,10 @@ internal unsafe partial class FrozenObjectHeapManager
                     Debug.Assert(obj != null);
                 }
             } // end of m_Crst lock
+            finally
+            {
+                m_Crst.Release();
+            }
 
             IntPtr result = (IntPtr)obj;