Add PredefinedOnly to Windows

Author: tqiu8

src/libraries/System.Private.CoreLib/src/System/Globalization/GlobalizationMode.Unix.cs

@@ -11,7 +11,7 @@ internal static partial class GlobalizationMode
 
         internal static bool UseNls => false;
 
-        internal static bool PredefinedOnly { get; } = GetSwitchValue("System.Globalization.PredefinedOnly", "DOTNET_SYSTEM_GLOBALIZATION_PREDEFINED_ONLY");
+        internal static bool PredefinedOnly { get; } = GetPredefinedOnly();
 
         private static bool GetGlobalizationInvariantMode()
         {

src/libraries/System.Private.CoreLib/src/System/Globalization/GlobalizationMode.Windows.cs

@@ -9,6 +9,8 @@ internal static partial class GlobalizationMode
         // So we need Invariant to be initialized first.
         internal static bool Invariant { get; } = GetInvariantSwitchValue();
 
+        internal static bool PredefinedOnly { get; } = GetPredefinedOnly();
+
         internal static bool UseNls { get; } = !Invariant &&
             (GetSwitchValue("System.Globalization.UseNls", "DOTNET_SYSTEM_GLOBALIZATION_USENLS") ||
                 !LoadIcu());

src/libraries/System.Private.CoreLib/src/System/Globalization/GlobalizationMode.cs

@@ -14,6 +14,9 @@ private static bool GetInvariantSwitchValue() =>
         private static bool TryGetAppLocalIcuSwitchValue([NotNullWhen(true)] out string? value) =>
             TryGetStringValue("System.Globalization.AppLocalIcu", "DOTNET_SYSTEM_GLOBALIZATION_APPLOCALICU", out value);
 
+        internal static bool GetPredefinedOnly() =>
+            GetSwitchValue("System.Globalization.PredefinedOnly", "DOTNET_SYSTEM_GLOBALIZATION_PREDEFINED_ONLY");
+
         private static bool GetSwitchValue(string switchName, string envVariable)
         {
             if (!AppContext.TryGetSwitch(switchName, out bool ret))