Fail when detecting ambiguous asset references

[Josharias]

Current Status

When referencing assets, for instance tile textures in a block definition, these asset references do not always include a module identifier but are sometimes referenced solely by their name. In module combinations with assets that share the same name, this can be a problem as the game does not know which asset to pick.

Currently, the resolution of ambiguous asset references is buggy and results in weird behavior. This can be reproduced by locally reverting the fix provided in #1934. By now the respective block definitions reside in CoreAssets. Detailed reproduction steps and screenshots of the issue are provided below:

How to Reproduce

1. Start a new Terasology CoreGameplay world with PlantPack enabled and memorize the seed.
2. Find an oak tree, memorize where you found it (e.g. via coordinates accessible via F3) and observe it's side texture
3. Replace the CoreAssets: prefix in OakTrunk.block with PlantPack:
4. Start a new Terasology CoreGameplay world with the same seed as before and PlantPack still enabled
5. Find the same oak tree as before and observe that the side texture is the same as before
6. Replace the value in OakTrunk.block with OakBark
7. Start a new Terasology CoreGameplay world with the same seed as before and PlantPack still enabled
8. Find the same oak tree as before and observe that the side texture is not the same as before

CoreAssets::OakTrunk.block with "tile": "CoreAssets:OakBark"

CoreAssets::OakTrunk.block with "tile": "PlanPack:OakBark"

CoreAssets::OakTrunk.block with "tile": "OakBark"

Desired Status

If multiple modules provide assets with the same name, the game is expected to be confused. Theoretically, it should at least pick one of the available assets with the referenced name and not, as it seems to be the case currently, pick an arbitrary other asset to use.

Practically, we want to avoid ambiguous situations and always prefix asset references with the respective module.
Hence, it would be even better to fail the world creation with a reasonable error message when noticing an asset reference that is missing a module prefix and may lead to ambiguity.