Throw error on mods without `fabric.mod.json`

I accidentally put my fabric.mod.json in the wrong folder, causing it to not appear in the jar. Instead of throwing an error, loom caused cryptic error messages in a different mod in the form error: cannot access class_${intermediate_id}: class file for net.minecraft.class_${intermediate_id} not found.

• modImplementation should throw an error when receiving a .jar without fabric.mod.json.
• loom should throw an error when attempting to build a .jar without a fabric.mod.json.

[zml2008]

no - the mod* configurations aim to mirror standard gradle configurations, and library is not a standard gradle configuration

[yyny]

@zml2008 There could be a modLibrary "..." then for jars that don’t have a fabric.mod.json. I think there will definitely be people that need jars without fabric.mod.json, but that should be opt-in, not opt-out.