Fix ClientCommandSourceStack crashing or returning improper values for certain method calls

[pupnewfster]

• Reimplement ClientCommandSourceStack#suggestRegistryElements for advancements based on the list of visible advancements on the client (fixes a regression/addresses a TODO from the port to 1.21.2. The other part for recipes, I didn't fix as I don't think there is any way to suggest recipe names on the client as it no longer receives them)
• Added an override for ClientCommandSourceStack#enabledFeatures to provide the enabled features instead of throwing a NPE due to server being null.
• Made ClientCommandSourceStack#sendSuccess properly make use of the CommandSource's settings and if the command source stack is set to silent. Now it just calls super, but explicitly marks that the success should not be sent to admins. This way we won't have to worry about divergence in our copy if vanilla makes any changes.
• Slightly cleaned up implementation by making everything just go through the connection instead of some things go through Minecraft#getInstance's copy of various fields (for example levels), and hiding the fact that it technically can be nullable to reduce overall warnings when viewing the code.

[neoforged-pr-publishing]

• Publish PR to GitHub Packages

Last commit published: 788ddb1821b8a1ca84640856a9124691ffceaeda.

PR Publishing

The artifacts published by this PR:

• 📦 net.neoforged:neoforge:21.4.80-beta-pr-1928-client_command_features
• 📦 net.neoforged:testframework:21.4.80-beta-pr-1928-client_command_features

Repository Declaration

In order to use the artifacts published by the PR, add the following repository to your buildscript:

repositories {
    maven {
        name 'Maven for PR #1928' // https://github.com/neoforged/NeoForge/pull/1928
        url 'https://prmaven.neoforged.net/NeoForge/pr1928'
        content {
            includeModule('net.neoforged', 'neoforge')
            includeModule('net.neoforged', 'testframework')
        }
    }
}

MDK installation

In order to setup a MDK using the latest PR version, run the following commands in a terminal.
The script works on both *nix and Windows as long as you have the JDK bin folder on the path.
The script will clone the MDK in a folder named NeoForge-pr1928.
On Powershell you will need to remove the -L flag from the curl invocation.

mkdir NeoForge-pr1928
cd NeoForge-pr1928
curl -L https://prmaven.neoforged.net/NeoForge/pr1928/net/neoforged/neoforge/21.4.80-beta-pr-1928-client_command_features/mdk-pr1928.zip -o mdk.zip
jar xf mdk.zip
rm mdk.zip || del mdk.zip

To test a production environment, you can download the installer from here.