Rename `pack.mcmeta` to be unique between Resource- & Datapack

The current situation of resource- and data packs being stored in separate folders, makes it harder to distribute creations as a pair. By allowing different naming conventions for their respective .mcmeta files such as the following would enable both assets and data to exist within a single folder:

• resourcepack.mcmeta (for resource packs)

• datapack.mcmeta (for data packs)

With this change the game could then identify which .mcmeta file to read, simplifying the distribution and organization of combined packs.
Altogether this might be the best way to both allow separated assets and data as well as combined ones.

PS: You could also just combine the pack_format (version) from now on to make the `pack.mcmeta` file between resource- and data pack IDENTICAL!