[linker] Method decorated with System.Runtime.Serialization.*Attribute must be marked...

[linker] Method decorated with System.Runtime.Serialization.*Attribute must be marked, Fixes #40574

Some serialization attributes are unlikely to have direct reference,
from IL, but will be needed at runtime to correctly serialize (or
deserialize) objects.

* OnDeserializedAttribute
* OnDeserializingAttribute
* OnSerializedAttribute
* OnSerializingAttribute

This, along with aad627c5e8ddf15397c87fa2d3e18b54f929c927, fixed bug
40574. The later part will have new unit tests in XI.

references:
https://bugzilla.xamarin.com/show_bug.cgi?id=40574