chore: Add new Manifest.kind for build.gradle.kts files (#406)

- [x] I ran `make setup && make` to update the generated code after
editing a `.atd` file (TODO: have a CI check)
- [x] I made sure we're still backward compatible with old versions of
the CLI.
For example, the Semgrep backend need to still be able to *consume* data
	  generated by Semgrep 1.50.0.
See
https://atd.readthedocs.io/en/latest/atdgen-tutorial.html#smooth-protocol-upgrades
	  Note that the types related to the semgrep-core JSON output or the
	  semgrep-core RPC do not need to be backward compatible!
- [ ] Any accompanying changes in `semgrep-proprietary` are approved and
ready to merge once this PR is merged

Author: TikhonJelvis

semgrep_output_v1.atd

@@ -2493,6 +2493,8 @@ type manifest_kind
   (* A Gradle build.gradle build file
    * https://docs.gradle.org/current/userguide/build_file_basics.html *)
   | BuildGradle
+  (* A Gradle build.gradle.kts file, which uses Kotlin instead of Groovy. *)
+  | BuildGradleKts
   (* A Gradle settings.gradle file
    * https://docs.gradle.org/current/userguide/settings_file_basics.html.
    * Multi-project builds are defined by settings.gradle rather than