Reorg semgrep_output_v1.atd (#322)

- [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 1.17.0.
See
https://atd.readthedocs.io/en/latest/atdgen-tutorial.html#smooth-protocol-upgrades

Author: aryx