[iOS] Fixes state restoration not work

[zhongwuzw]

Actually, the coder of decodeRestorableStateWithCoder in FlutterViewController seems is not support to use encode/decodeDataObject, it would throw exception. So we changed to bytes encoded.

Exception occurred restoring state value for key '$0' was of unexpected class 'NSMutableData' (0x1db4082a8) [/System/Library/Frameworks/CoreFoundation.framework].
Allowed classes are:
 {(
)}

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[chinmaygarde]

Can you describe or link the issue please?

[chinmaygarde]

The patch does look fine to me. I am just not sure what issue it is cross referenced to.

[zhongwuzw]

The patch does look fine to me. I am just not sure what issue it is cross referenced to.

@chinmaygarde We added the feature of state restoration on iOS, but when we enable it and restore the state, it crashes and throws the exception like below. State restoration decoder seems can't use the decodeDataObject method, so we need to change to bytes encoded.

Exception occurred restoring state value for key '$0' was of unexpected class 'NSMutableData' (0x1db4082a8) [/System/Library/Frameworks/CoreFoundation.framework].
Allowed classes are:
 {(
)}