Camel case support for MessagePack.

1. Contractless camel case serialization of properties to MessagePack map keys.
2. Dynamic serialization of enum values to string literals using MessagePack's DynamicEnumAsStringResolver.
3. Dynamic case insensitive deserialization of MessagePack map keys and of string literals to Enum values.

Made to match naming conventions of System.Text.Json.JsonSerializerDefaults.Web.

Api

Use:

• CamelCaseContractlessFormatterResolver.Instance for all the features,
• CamelCaseAllowingDynamicEnumAsStringFormatter<T>.Instance for just enums,
• CamelCaseContractlessMapFormatter<T>.Instance for just maps.

Formatter<T>.Instance are null where T is not suitable for use with given Formatter.