Add SQLx query files as generated

[mercxry]

Mark **/.sqlx/query-*.json files as generated and added a test for it.

Description

SQLx is a Rust SQL library (11.4k stars) which generates **/.sqlx/query-*.json files in offline mode (enabled by default).
These are used to be able to compile a project without requiring the development database to be online.

I would like Github to automatically hide these files from diffs, since it could generate lots of files and it's a bit annoying to hide them manually one by one in each PR.

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=path%3A**%2F.sqlx%2Fquery-*.json+NOT+is%3Afork
  • I have included a real-world usage sample for all extensions added in this PR:
    • Sample source(s):
      • https://github.com/rust-lang/docs.rs/blob/master/.sqlx/query-2b8b1aae3740a05cb7179be9c7d5af30e8362c3cba0b07bc18fa32ff1a2232cc.json
    • Sample license(s): MIT
  • I have included a change to the heuristics to distinguish my language from others using the same extension.