Retro-add the dll files of the project manually for older versions

[Chingling152]

Summary

Retro-add the compiled DLL files of the project to support consumers using older versions.

Motivation

In some cases, having direct access to the compiled DLL files is necessary or better than using NuGet.

Proposed Change

Generate the compiled DLLs for the relevant target frameworks supported by older versions.

Benefits

Enables usage of the project without the need of a package restore tooling.