Feature request: Support disassembling older tfms' dlls

This is a feature request to add a dropdown box where I can select which dll I want to disassemble. This would not change the disassembler used, but it would instead just change which dll it uses, for example I could select net6.0 and it would decompile my net6.0 dll with the .NET 7.0 disassembler.

This would be very useful to me as I often write very multi-tfm code, with lots of `#if`s. It would be most useful to quickly check my net6.0 dll probably actually produces good vectorised code, since in .NET 7+ I am using the new operations on the vector types mostly, therefore this part of my code shares very few similarities between .NET 7 and .NET 6.

Another use would be if the library doesn't support .NET 7 directly, but you want to check what the codegen would be on .NET 7 to see if it should be specialised.

Thanks for making a great extension btw!