(Suggestion) Use JSON patches for MultiMC instances

[NeRdTheNed]

This allows changing the Minecraft version in the instance without re-editing the component, and easier interoperability with other MultiMC features. More information about JSON patches can be found on the MultiMC wiki page about them. Here is a MultiMC instance demonstrating this.

Instructions:

• Create a new MultiMC instance.

• Click "Edit Instance".

• Click "Add Empty". Enter "LaunchWrapper" for the name, and "org.mcphackers.launchwrapper" for the UUID.

• Select the new component labeled "LaunchWrapper", and click "Edit".

• Replace the contents of the file with something like this:

  {
  "+traits": [
      "noapplet"
  ],
  "assetIndex": {
      "id": "empty",
      "sha1": "62ea787c1f800c091b98678b050453a5ae59d7bc",
      "size": 14,
      "totalSize": 0,
      "url": "https://mcphackers.github.io/assets/empty.json"
  },
  "libraries": [
      {
          "name": "org.mcphackers:launchwrapper:1.0",
          "url": "https://mcphackers.github.io/libraries/"
      },
      {
          "name": "org.ow2.asm:asm:9.2",
          "url": "https://repo1.maven.org/maven2/"
      },
      {
          "name": "org.ow2.asm:asm-tree:9.2",
          "url": "https://repo1.maven.org/maven2/"
      },
      {
          "name": "org.json:json:20230311",
          "url": "https://mcphackers.github.io/libraries/"
      },
      {
          "name": "org.mcphackers.rdi:rdi:1.0",
          "url": "https://mcphackers.github.io/libraries/"
      }
  ],
  "mainClass": "org.mcphackers.launchwrapper.Launch",
  "minecraftArguments": "--username ${auth_player_name} --session ${auth_session} --gameDir ${game_directory} --assetsDir ${game_assets}",
  "requires": [
      {
          "uid": "net.minecraft"
      }
  ],
  "formatVersion": 1,
  "name": "LaunchWrapper",
  "uid": "org.mcphackers.launchwrapper",
  "version": "1.0.0"
  }

  The existing version-specific information about creating a MultiMC instance should apply here (minecraftArguments should be customised as needed, assetIndex and noapplet can be removed for Minecraft 1.6 and onwards etc). The main difference between this and the existing instructions is that the format of the libraries array is different for JSON patches (url is treated like a maven repo).

• Save and close the document.

This should produce an instance similar to the attached one. I also edited mmc-pack.json to set dependencyOnly to be true on the LaunchWrapper patch, which prevents disabling it (optional).

[Lassebq]

So, I'm not too sure, but does this issue suggest replacing MultiMC install guide with this? If so, could you please make it into a pull request? Thanks.

[Lassebq]

Due to my decision of not shipping versioned releases (until launchwrapper is stable) this method is now broken, as MultiMC derivatives (in my case Prism Launcher) fail with this error message:

Instance update failed because: Game update failed: it was impossible to fetch the required libraries.

This is due to library that I am trying to use not being in any remote repositories and therefore I had to get rid of "url" parameter.

[Lassebq]

A temporary workaround is to run the game in "Offline mode", which prevents libraries from being checked. But until a better solution is found, this issue remains open

[Lassebq]

Turns out it just needs an empty

            "downloads": {
            },

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