We should move src/mono/System.Private.CoreLib/src/ILLink/ILLink.LinkAttributes.xml to a shared location and make various attribute removal conditional on feature switches that SDKs (or end users) can opt into.

The list currently has things in it that are known to cause behavioral differences in XmlSerializer (ObsoleteAttribute) or Entity Framework (the nullable annotations cruft). While this is likely fine for WASM, broken Entity Framework will likely be unacceptable for Xamarin.

Without feature switches, the workarounds for someone wanting to keep the stripped attributes are pretty laborious.