Command to check for missing translations

[asvae]

We need a command to check if some translation strings are not being used.

Note that translation strings are always used without variables. I.e. offsets.sizes.xl will never be used as offsets.sizes.${size}. If not - that's a mistake.

Command should just display a list of unused strings separated by line break. Should not attempt removing these strings.

[m0ksem]

I think we can close it since we use vue18n-unused.

[asvae]

Irrelevant because #3425