Add SARIF as JSON alias

[orhantoy]

SARIF files are currently rendered as plain-text on GitHub. This PR improves that experience by introducing an alias to JSON.

Checklist:

• I am adding a new extension to a language.
  • The new extension is used in hundreds of repositories on GitHub.com
    • Search results for each extension:
      • https://github.com/search?type=code&q=NOT+is%3Afork+path%3A*.sarif+level
  • I have included a real-world usage sample for all extensions added in this PR:
    • Sample source: https://docs.github.com/en/code-security/code-scanning/integrating-with-code-scanning/sarif-support-for-code-scanning#example-showing-all-supported-sarif-properties
    • Sample license: https://docs.github.com/en/site-policy/github-terms/github-terms-of-service#c-acceptable-use
  • I have included a change to the heuristics to distinguish my language from others using the same extension.

[lildude]

LGTM. Thanks.

Note: this PR will not be merged until close to when the next release is made. See here for more details.