Dim disabled Save button in custom folder sync prefs dialog

Fixes #3664

Signed-off-by: Chris Narkiewicz <hello@ezaquarii.com>

src/main/java/com/owncloud/android/ui/dialog/SyncedFolderPreferencesDialogFragment.java

@@ -195,10 +195,10 @@ public class SyncedFolderPreferencesDialogFragment extends DialogFragment {
         mUploadBehaviorSummary = view.findViewById(R.id.setting_instant_behaviour_summary);
 
         mCancel = view.findViewById(R.id.cancel);
-        mCancel.setTextColor(accentColor);
+        ThemeUtils.themeDialogActionButton(mCancel);
 
         mSave = view.findViewById(R.id.save);
-        mSave.setTextColor(accentColor);
+        ThemeUtils.themeDialogActionButton(mSave);
 
         // Set values
         setEnabled(mSyncedFolder.getEnabled());

src/main/java/com/owncloud/android/utils/ThemeUtils.java

@@ -40,6 +40,7 @@ import android.widget.ProgressBar;
 import android.widget.SeekBar;
 import android.widget.TextView;
 
+import com.google.android.material.button.MaterialButton;
 import com.google.android.material.floatingactionbutton.FloatingActionButton;
 import com.google.android.material.snackbar.Snackbar;
 import com.google.android.material.textfield.TextInputLayout;
@@ -419,6 +420,24 @@ public final class ThemeUtils {
         ));
     }
 
+    public static void themeDialogActionButton(MaterialButton button) {
+        if (button == null ) return;
+
+        Context context = button.getContext();
+        int accentColor = ThemeUtils.primaryAccentColor(button.getContext());
+        int disabledColor = ContextCompat.getColor(context, R.color.disabled_text);
+        button.setTextColor(new ColorStateList(
+            new int[][]{
+                new int[] { android.R.attr.state_enabled}, // enabled
+                new int[] {-android.R.attr.state_enabled}, // disabled
+            },
+            new int[]{
+                accentColor,
+                disabledColor
+            }
+        ));
+    }
+
     public static void themeEditText(Context context, EditText editText, boolean themedBackground) {
         if (editText == null) { return; }