Use GetInt32ComPlusOrDotNetConfig and don't cache _stackSizeFromConfig

Author: Keegan Caruso

src/coreclr/nativeaot/System.Private.CoreLib/src/System/Threading/Thread.NativeAot.Unix.cs

@@ -98,7 +98,7 @@ private unsafe bool CreateThread(GCHandle thisThreadHandle)
 
             if (stackSize <= 0)
             {
-                stackSize = _stackSizeFromConfig;
+                stackSize = GetDefaultStackSize();
             }
 
             if (!Interop.Sys.CreateThread((IntPtr)stackSize, &ThreadEntryPoint, (IntPtr)thisThreadHandle))

src/coreclr/nativeaot/System.Private.CoreLib/src/System/Threading/Thread.NativeAot.Windows.cs

@@ -182,7 +182,7 @@ private unsafe bool CreateThread(GCHandle thisThreadHandle)
 
             if (stackSize <= 0)
             {
-                stackSize = _stackSizeFromConfig;
+                stackSize = GetDefaultStackSize();
             }
 
             if ((0 < stackSize) && (stackSize < AllocationGranularity))

src/coreclr/nativeaot/System.Private.CoreLib/src/System/Threading/Thread.NativeAot.cs

@@ -483,18 +483,16 @@ private static void StopThread(Thread thread)
             }
         }
 
-        private static int _stackSizeFromConfig = GetDefaultStackSize();
-
         internal static int GetDefaultStackSize()
         {
             // Keep the same arbitrary minimum and maximum from the coreclr\vm layer.
             // The max was 0x80000000 (2G).
             // This is checked by the value being parsed into an int32.
             const uint minStack = 0x10000;     // 64K
 
-            int sizeFromConfig = AppContextConfigHelper.GetInt32Config(
+            int sizeFromConfig = AppContextConfigHelper.GetInt32ComPlusOrDotNetConfig(
                 "System.Threading.DefaultStackSize",
-                "DOTNET_Threading_DefaultStackSize",
+                "Threading_DefaultStackSize",
                 0,
                 false);