[Swift Language Features] Generate correct Dispose for non-frozen structs and generic types

[jkurdek]

Non frozen structs and generic types are projected as classes. We need to manualy release all the resources in the dispose method. We need to learn what needs disposing and genearte an appropriate Dispose method.

By projecting non-frozen types and generics as classes, we allow them to have destructors. The problem is that without knowing their memory layout, we don’t know what needs to be released in the destructor.

For example, consider Swift.String:

  store ptr %2, ptr %str.debug._guts._object._object, align 8, !dbg !136
  call void @swift_bridgeObjectRelease(ptr %2) #5, !dbg !137

The value witness table might actually resolve this without requiring explicit knowledge of the layout:
https://github.com/swiftlang/swift/blob/b185bf9562f007c37acdfcdbe42eebfd96bd9973/include/swift/ABI/ValueWitness.def#L114

This is something we will investigate further.

Originally posted by @kotlarmilos in #2970