Add source collision test, rust_bindgen doc.

Bug: 159064919
Test: Soong tests pass (and fail if error is modified).
Change-Id: Id4f76e53e11e46ae495f9613a2699c598e7daea4
diff --git a/rust/Android.bp b/rust/Android.bp
index 26a5a08..e03bf4f 100644
--- a/rust/Android.bp
+++ b/rust/Android.bp
@@ -27,6 +27,7 @@
     testSrcs: [
         "binary_test.go",
         "bindgen_test.go",
+        "builder_test.go",
         "clippy_test.go",
         "compiler_test.go",
         "coverage_test.go",