The SMT-LIB language already hash Z3 as an interpreter, but doesn't recognize the extension *.z3 as valid

Description

The Z3 interpreter was already being used, but not the extension.

It is not used in any other languages.

Checklist:

• I am adding a new extension to a language.
  • The new extension is used in hundreds of repositories on GitHub.com (235M Repositories) (7.6K files)
    • Search results for each extension:
      • https://github.com/search?type=code&q=NOT+is%3Afork+path%3A*.z3
      • • I have included a real-world usage sample for all extensions added in this PR:
    • Sample source(s):
      • [URL to each sample source, if applicable]
    • Sample license(s): MIT