netfx: add conditional branches for .NET Framework targets

Recently added Git credential protocol enhancements used new BCL APIs
that are not present in .NET Framework, which we still target for
Windows. Add conditionally compiled versions for .NET Framework targets.

Signed-off-by: Matthew John Cheetham <mjcheetham@outlook.com>

Author: mjcheetham

src/shared/Core/GitCapabilities.cs

@@ -114,8 +114,11 @@ public static IEnumerable<string> ToProtocolNames(GitCapabilities capabilities)
         {
             yield break;
         }
-
+#if NETFRAMEWORK
+        foreach (GitCapabilities flag in (GitCapabilities[])Enum.GetValues(typeof(GitCapabilities)))
+#else
         foreach (GitCapabilities flag in Enum.GetValues<GitCapabilities>())
+#endif
         {
             if (flag == GitCapabilities.None)
             {

src/shared/Core/GitResponse.cs

@@ -180,7 +180,11 @@ public static GitResponse Yield() =>
     /// silently no-ops and this view stays empty.
     /// </para>
     /// </remarks>
+#if NETFRAMEWORK
+    public IReadOnlyDictionary<string, string> State => _stateView ??= new ReadOnlyDictionary<string, string>(_state);
+#else
     public IReadOnlyDictionary<string, string> State => _stateView ??= _state.AsReadOnly();
+#endif
 
     /// <summary>
     /// Set a single state entry.