encoding/openapi: supported nested definitions

Change-Id: I2c79b5d02fdc9ac22fa93f5e06be46f73cf0be51
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/5341
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>
diff --git a/encoding/openapi/testdata/nested.cue b/encoding/openapi/testdata/nested.cue
new file mode 100644
index 0000000..f1343e0
--- /dev/null
+++ b/encoding/openapi/testdata/nested.cue
@@ -0,0 +1,8 @@
+package foo
+
+Struct :: {
+	T :: int
+
+	a?: T
+	b?: T
+}