Add .code-snippets as a JSONC extension

[Nixinova]

• Resolve Proposal: Add .code-snippets #5574

Description

Adds .code-snippets to the list of JSONC filenames.
The files are used by vscode.
Proof it's JSONC (love the new search, shame its only got a 100-file limit atm)

Checklist:

• I am associating a language with a new file extension.
  • The new extension is used in hundreds of repositories on GitHub.com
    • Search results for each extension:
      • extension:code-snippets - 21K+
  • I have included a real-world usage sample for all extensions added in this PR:
    • Sample source: file, with the code uncommented
    • Sample license: MIT
  • I have included a change to the heuristics to distinguish my language from others using the same extension.