Replace lockfile with dependency source in targets (#362)

- [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!

Author: mmcqd

semgrep_output_v1.atd

@@ -2092,7 +2092,7 @@ type analyzer <ocaml attr="deriving show"> = string wrap <ocaml module="Analyzer
 *)
 type target <ocaml attr="deriving show"> = [
   | CodeTarget of code_target
-  | LockfileTarget of lockfile
+  | DependencySourceTarget of dependency_source
 ]
 
 (*
@@ -2109,7 +2109,7 @@ type code_target <ocaml attr="deriving show"> = {
   *)
   analyzer: analyzer;
   products: product list;
-  ?lockfile_target: lockfile option;
+  ?dependency_source: dependency_source option;
 }
 
 type scanning_roots <ocaml attr="deriving show"> = {