Add paket-unity UPM mode [ATLAS-1273]

[Joaquimmnetto]

Description

Paket packages can now be configured to be installed as UPM packages. This can be useful when your paket package contains an UPM one (with a package.json file), and you want it to be integrated with Unity's packages folder.

This mode sets the installation directory (paketOutputDirectoryName) to the unity project's Packages folder, and ensures that the package.jsonfile for each dependency is in the installed package root.

If an installed package is not UPM-compatible, that is, it doesn't have a package.json file, such file will be created. By default, a package.json is generated with com.wooga.nuget.${paketPackage.toLowerCase()} name, and version 0.0.0, but those can be overridden and more properties can be added on using the mappings in paketUpmPacakgeJson.

UPM mode can be enabled through the paketUpmPackageEnabled property, or using the paketUnity.enablePaketUpmPackages() extension method. It is disabled by default.

Changes

• Packages can now be installed in UPM mode in paket-unity plugin
• UPM mode in PaketUnityInstall task
• paketUpmPackageEnabled and paketUpmPacakgeJson properties to PaketUnityPluginExtension

[Azurelol]

There's a typo, an s at the end?

[Joaquimmnetto]

Its not a typo, there may be many manifests. Its a map of [paket_name: upm manifest] after all.

[pletoss]

lgtm.

I have one concern i'd like to clarify first before merging. please see comment directly in code.

[pletoss]

one thing that we need to make sure is, that ONLY whatever was being installed in Assets/Paket.Unity3D gets installed in Packages/ too, and nothing more. So if there is any dependency of something referenced in the unity3d reference file but it would have NOT be installed in there, it should not be installed in Packages either.

My concern is to remind you that paket actually only copies the .net dll variants that are defined/supported inside Paket.Unity3D.

[Joaquimmnetto]

@pletoss this task is the exact same one the installs stuff in Assets/Paket.Unity3D. All I'm doing there is changing the installation directory and making sure that the package.json file is in the right place. So don't worry about this ;)