chore(sca): add rpc to match subprojects (#364)

Adds an RPC type that allows Python to ask Ocaml to match subprojects
based on a list of dependency source files.
This will allow us to switch to ocaml-based subproject matching
independently from the rest of file targeting.

- [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: bkettle

semgrep_output_v1.atd

@@ -2382,6 +2382,7 @@ type sca_error = [
  * Used as the unit of analysis for supply chain.
  *)
 type subproject
+    <ocaml attr="deriving show">
     <python decorator="dataclass(frozen=True, order=True)"> =
 {
     root_dir: fpath;
@@ -2554,6 +2555,7 @@ type function_call <python decorator="dataclass(frozen=True)"> = [
   (* for now, the transitive reachability filter takes only a single dependency graph as input.
    * it is up to the caller to call it several times, one for each subproject *)
   | CallTransitiveReachabilityFilter of transitive_reachability_filter_params
+  | CallMatchSubprojects of fpath list
 ]
 
 (* ----------------------------- *)
@@ -2573,6 +2575,7 @@ type function_return <python decorator="dataclass(frozen=True)"> = [
   | RetDumpRulePartitions of bool
   | RetTransitiveReachabilityFilter of transitive_finding list
   | RetGetTargets of target_discovery_result
+  | RetMatchSubprojects of subproject list
 ]
 
 (*****************************************************************************)