[Swift ABI compatibility] Implement correct memory handling in C# bindings

[kotlarmilos]

Tasks

• [Swift ABI compatibility] Document memory ownership and handling at the Swift–C# boundary #3008
• [Swift ABI compatibility] Functional tests for InitWithCopy and Destroy functions in value witness table #3009
• [Swift language features] Retain result in the generated Swift async wrapper #3020
• [Swift ABI compatibility] Refactor projection tooling to project value types with ref properties as C# classes #3035
• [Swift ABI compatibility] Refactor projected C# classes to invoke Destroy function #3036
• [Swift language features] Use canonical Dispose pattern in the generated bindings #2978
• [Swift language features] Revisit thread safety of ref counting in projections #2975
• [Swift language features] Improve MarshalToSwift to track size of buffer in parameter #2974
• [Swift ABI compatibility] Implement Swift payload as SafeHandler to decouple IDisposable from the bindings #3018