Suggestion: Provide .unitypackage deployment

[applejag]

Description

Deploying as unity package is nice if you dont want to struggle with the Unity Package Manager.

The package would basically be a zip of the /Plugins files of the package. Deployed as a .unitypackage file ready for download. The package file can be read by Unity and imported they way.

Why we need this

For users comfort.

Suggested solution

The package would just unpack as the plugins folder, i.e. Plugins/Newtonsoft [Editor/Aot/Portable]/*.dll.

Nice to have would be a embedded installation modal asking if you wish to transfer to using the UPM version of the package.

[applejag]

In light of this new Package Installer Creator tool by @needle-tools, given their permission, I could just use that and package that in the release.

[applejag]

This had to be forwarded to 12.0.303 as the changes from #54 were too important to delay further.