[1.21.3] Fix blocks sometimes missing ambient occlusion

[XFactHD]

This PR fixes blocks sometimes missing ambient occlusion on a vertical or horizontal face (depends on orientation).
The caveat behind this fix is that it reverts the AO fix implemented in #1370, which is why I'm opening this as a draft for now.

Fixes #1613.

[neoforged-pr-publishing]

• Publish PR to GitHub Packages

Last commit published: d146bf9d1b9e6dc1b79737e57e7aafaaf158e7a4.

PR Publishing

The artifacts published by this PR:

• 📦 net.neoforged:testframework:21.3.2-beta-pr-1618-block_shadows
• 📦 net.neoforged:neoforge:21.3.2-beta-pr-1618-block_shadows

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 #1618' // https://github.com/neoforged/NeoForge/pull/1618
        url 'https://prmaven.neoforged.net/NeoForge/pr1618'
        content {
            includeModule('net.neoforged', 'testframework')
            includeModule('net.neoforged', 'neoforge')
        }
    }
}

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-pr1618.
On Powershell you will need to remove the -L flag from the curl invocation.

mkdir NeoForge-pr1618
cd NeoForge-pr1618
curl -L https://prmaven.neoforged.net/NeoForge/pr1618/net/neoforged/neoforge/21.3.2-beta-pr-1618-block_shadows/mdk-pr1618.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.