Vendor dependencies

Let's see how I like this workflow.

vendor/cxx/tests/ui/array_len_expr.rs

@@ -0,0 +1,10 @@
+#[cxx::bridge]
+mod ffi {
+    struct Shared {
+        arraystr: [String; "13"],
+        arraysub: [String; 15 - 1],
+        arrayzero: [String; 0],
+    }
+}
+
+fn main() {}