Crash due to Parcelable problem
Crash when restoring AccountSetupBasics instance state

Steps to reproduce the behavior:
1. In developer options: enable don't keep activities" to easily reproduce the bug
2. Go to AccountSetupBasics activity
3. Click home button to quit the app
4. Use recent app to go back to K9
5. The app crash

**Environment (please complete the following information):**
 - K-9 Mail version: [5.725]
 - Android version: [10]
 - Device: [Tablet ordissimo celia]

I suspect the parcelable part in FoldableLinearLayout

**Logs**
2020-12-22 15:11:54.427 15426-15426/com.fsck.k9.debug E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.fsck.k9.debug, PID: 15426
    java.lang.RuntimeException: Parcel android.os.Parcel@3b63efa: Unmarshalling unknown type code 2131362261 at offset 1852
        at android.os.Parcel.readValue(Parcel.java:2945)
        at android.os.Parcel.readSparseArrayInternal(Parcel.java:3329)
        at android.os.Parcel.readSparseArray(Parcel.java:2484)
        at android.os.Parcel.readValue(Parcel.java:2923)
        at android.os.Parcel.readArrayMapInternal(Parcel.java:3246)
        at android.os.BaseBundle.initializeFromParcelLocked(BaseBundle.java:292)
        at android.os.BaseBundle.unparcel(BaseBundle.java:236)
        at android.os.Bundle.getSparseParcelableArray(Bundle.java:1029)
        at com.android.internal.policy.PhoneWindow.restoreHierarchyState(PhoneWindow.java:2156)
        at android.app.Activity.onRestoreInstanceState(Activity.java:1590)
        at com.fsck.k9.activity.setup.AccountSetupBasics.onRestoreInstanceState(AccountSetupBasics.java:119)
        at android.app.Activity.performRestoreInstanceState(Activity.java:1545)
        at android.app.Instrumentation.callActivityOnRestoreInstanceState(Instrumentation.java:1353)


diff --git a/app/ui/legacy/src/main/java/com/fsck/k9/view/FoldableLinearLayout.java b/app/ui/legacy/src/main/java/com/fsck/k9/view/FoldableLinearLayout.java
index 997167a64..5d0e84ae8 100644
--- a/app/ui/legacy/src/main/java/com/fsck/k9/view/FoldableLinearLayout.java
+++ b/app/ui/legacy/src/main/java/com/fsck/k9/view/FoldableLinearLayout.java
@@ -121,9 +121,9 @@ public class FoldableLinearLayout extends LinearLayout {
         }
     }
 
-    static class SavedState extends BaseSavedState {
+    public static class SavedState extends BaseSavedState {
 
-        static final Parcelable.Creator<SavedState> CREATOR =
+        public static final Parcelable.Creator<SavedState> CREATOR =
                 new Parcelable.Creator<FoldableLinearLayout.SavedState>() {
 
             @Override
['app/ui/legacy/src/main/java/com/fsck/k9/view/FoldableLinearLayout.java']