[1.7.10] Update & migrate to GNTH build script

[Pilzinsel64]

This PR updates the build script to the GTNH build script.

It enables us to use (but not forced) modern Java for development, for IDE and for testing the mod via pre-dfined gradlew stasks like runClient, runClient17 and runClient21. Same for Server and obfuscated client.

Changes

• Updates to GTNH build script
  • Adjust format of mcmod.info to be more up-to-date
  • Move the api package from src/api/... to src/main/.../api
• Use CI workflows from 1.7.10 example mod maintaned by GTNH
• Fix minor errors prevent compiling the mod

[Pilzinsel64]

I'm still not sure why it marks the whole file as changed at f11b73e even if I just added or modified one line. 🤔 That normally doesn't happen.

[XCompWiz]

I'm still not sure why it marks the whole file as changed at f11b73e even if I just added or modified one line. 🤔 That normally doesn't happen.

I assume whitespace or line ending changes.