Clarify MobileFormatter collection type limitations in docs (#4822)

* Fix misleading docs claiming List<T> is serializable by MobileFormatter

Remove List<int> from the list of supported SerializationInfo types in
the CSLA 9 upgrade guide, and correct the serialization.md claim that
List<T> and Dictionary<K,V> are supported. These standard .NET
collection types are not directly serializable - users should use
MobileList<T> or MobileDictionary<K,V> from Csla.Core instead.

Fixes #4680

https://claude.ai/code/session_011R3Y2CSgCZrDwdVacjARaW

* Restore List<int> to SerializationInfo supported types list

CslaBinaryWriter/Reader explicitly handle List<int> (CslaKnownTypes.ListOfInt),
so it IS a valid type for use in custom serializers via SerializationInfo.AddValue.
Updated the warning to clarify that other generic collection types (List<string>,
Dictionary<K,V>, etc.) are not supported.

https://claude.ai/code/session_011R3Y2CSgCZrDwdVacjARaW

---------

Co-authored-by: Claude <noreply@anthropic.com>

Author: rockfordlhotka

docs/Upgrading to CSLA 9.md

@@ -166,6 +166,8 @@ This includes:
 * `char[]`
 * `List<int>`
 
+> ⚠️ Other generic collection types such as `List<string>`, `Dictionary<K,V>`, etc. are _not_ directly serializable by `SerializationInfo`. For serializable collections in business object properties, use `MobileList<T>` or `MobileDictionary<K,V>` from `Csla.Core`, or register a custom serializer for your type.
+
 If you look at the implementation of [PocoSerializer](https://github.com/MarimerLLC/csla/blob/main/Source/Csla/Serialization/Mobile/CustomSerializers/PocoSerializer.cs) you'll see that it relies on `System.Text.Json` to serialize and deserialize the object, and stores the JSON string in the `SerializationInfo` instance.
 
 The [ClaimsPrincipalSerializer](https://github.com/MarimerLLC/csla/blob/main/Source/Csla/Serialization/Mobile/CustomSerializers/ClaimsPrincipalSerializer.cs) type has two implementations.

docs/serialization.md

@@ -10,7 +10,9 @@ The default serializer for CSLA (version 6 and later) is `MobileFormatter`. This
 
 ### Using MobileFormatter
 
-MobileFormatter supports many basic .NET types, including "primitive" types like `int`, `string`, `DateTime`, etc. It also supports `List<T>`, `Dictionary<K,V>`, and other common collection types. It also supports any type that implements `IMobileObject`, which includes all CSLA base types.
+MobileFormatter supports many basic .NET types, including "primitive" types like `int`, `string`, `DateTime`, etc. It also supports any type that implements `IMobileObject`, which includes all CSLA base types.
+
+> ⚠️ Standard .NET collection types such as `List<T>` and `Dictionary<K,V>` are _not_ directly serializable by `MobileFormatter`. Use `MobileList<T>` or `MobileDictionary<K,V>` from `Csla.Core` for serializable collections, or register a custom serializer for your collection type.
 
 If you create your complex types by subclassing CSLA base types and using the managed property syntax, you don't need to do anything special to support serialization.