Should `ice2slice` Use the New `MetadataValidator`?

[InsertCreativityHere]

Currently ice2slice performs no validation of metadata.
I think it would be preferable to still validate metadata, even if it is 'different' from the other Slice compilers.
We could also co-opt the MetadataValidator to issue warnings for metadata that we can't map in new Slice.

[pepone]

How would you deal with language specific metadata, say for example cs:generic which we map to cs::type, or cs:namespace mapped to cs::namespace? I would be good if we can reuse the same validators from slice2cs.

[bernardnormier]

If ice2slice "translates" Ice metadata into Slice attributes, then it should validate the metadata it consumes. Currently it would be only cs metadata, in addition to non-language-specific metadata.