Validate `define-x` names

[Acaccia]

There is currently no checks on the validity of the names given in those functions:

• define-data-var
• define-map
• define-fungible-token
• define-non-fungible-token
• define-private
• define-public
• define-read-only
• define-trait (only trait name, methods names seem to be okay if they clash)

Here is a example of Clarity code that should fail:

>> (define-data-var map int 0)
error: Runtime Error: Runtime error while interpreting ST000000000000000000002AMW42H.contract-0: Unchecked(NameAlreadyUsed("map"))