Fixed Gradle build and some bugs

[Doenerstyle]

This PR should fix Gradle building by upgrading ForgeGradle 2.3 to anatawa12's fork and fixing >100 compilation errors. And while I was at it, I've also made some other improvements.

Changes I've made

• Upgraded to anatawa12's fork of ForgeGradle 2.3.
• Commented out a lot of the build.gradle. It builds for me, but I left the comments in there in case the code was more relevant/helpful than I thought.
• Updated the Minecraft mappings to stable_39 and updated the Java code accordingly.
• Fixed the Apple Leaves, Bamboo Leaves, and Cork Leaves all having broken textures either on fast or on fancy graphics settings. Apple Leaves and Cork Leaves now always use their fancy texture because their fast texture is and was broken.
• Made sure CraftTweaker code is only run when CraftTweaker is loaded (using ways we already used for other mods). The commit fef0a16 apparently made CraftTweaker a hard dependency, so I fixed that.
• Fixed the Cork Sapling having a buggy name.
• Fixed [1.12.2] Bee Boxes will only fill honey halfway #386.
• This should fix Forge maven links broke #370.
• Updated the Simplified Chinese localization as provided by @Chsier in GrowthCraft 4.2.2.1 does not generate villages in the main world with Growthcraft characteristic buildings such as vineyards. #385.
• Updated the README to fix some typos and match title and badges of the 1.20 repo, minus GH Actions.
• Updated the actions used in our GitHub workflows, though I believe they probably need to be reworked anyways?

The Build workflow fails in the sonarqube step, the build itself works fine.

I did not raise version numbers yet, though these changes should be released imho. I wanted to leave it up to you which number gets bumped for the next version.

I hope this update will allow for some more bugfixes to be implemented even for good old 1.12.2.