Rust: add experimental bazel target

Author: Paolo Tranquilli

rust/BUILD.bazel

@@ -46,10 +46,20 @@ codeql_pkg_files(
     ],
 )
 
-codeql_pack(
-    name = "rust",
-    srcs = [
-        ":root-files",
-        ":tools",
-    ],
-)
+[
+    codeql_pack(
+        name = "-".join(parts),
+        srcs = [
+            ":root-files",
+            ":tools",
+        ],
+        pack_prefix = "/".join(parts),
+    )
+    for parts in (
+        [
+            "experimental",
+            "rust",
+        ],
+        ["rust"],
+    )
+]