Add public implementation CultureDataSupport (#18691)

Author: luqunl

src/System.Private.CoreLib/System.Private.CoreLib.csproj

@@ -303,8 +303,8 @@
     <Compile Include="$(BclSourcesRoot)\Internal\Console.cs" />
     <Compile Condition="'$(FeatureCominterop)' == 'true'" Include="$(BclSourcesRoot)\Internal\Threading\Tasks\AsyncCausalitySupport.cs" />
     <Compile Condition="'$(FeatureCominterop)' == 'true'" Include="$(BclSourcesRoot)\Internal\Runtime\InteropServices\WindowsRuntime\ExceptionSupport.cs" />
-    <Compile Condition="'$(FeatureAppX)' == 'true'" Include="$(BclSourcesRoot)\Internal\Resources\WindowsRuntimeResourceManagerBase.cs" />
     <Compile Condition="'$(FeatureAppX)' == 'true'" Include="$(BclSourcesRoot)\Internal\Resources\PRIExceptionInfo.cs" />
+    <Compile Condition="'$(FeatureAppX)' == 'true'" Include="$(BclSourcesRoot)\Internal\Resources\WindowsRuntimeResourceManagerBase.cs" />
   </ItemGroup>
   <ItemGroup>
     <Compile Include="$(BclSourcesRoot)\System\Reflection\Assembly.CoreCLR.cs" />

src/System.Private.CoreLib/src/Internal/Resources/WindowsRuntimeResourceManagerBase.cs

@@ -21,5 +21,14 @@ public abstract CultureInfo GlobalResourceContextBestFitCultureInfo
         }
 
         public abstract bool SetGlobalResourceContextDefaultCulture(CultureInfo ci);
+
+        /// <summary>
+        /// Check whether CultureData exists for specified cultureName
+        /// This API is used for WindowsRuntimeResourceManager in System.Runtime.WindowsRuntime
+        /// </summary>
+        public static bool IsValidCulture(string cultureName)
+        {
+            return CultureData.GetCultureData(cultureName, /* useUserOverride */ true) != null;
+        }
     }
 }