[Rust] Ensure unions are referenced with the correct path (#6422)

* Add codegen test for namespaced unions

* [Rust] Handle cross-namespace union use

* [Rust] Test namespace handling

* [Rust] Drop trailing whitespace in codegen

* [Rust] Set flags in generate_code.bat to match .sh

* [C#] Add additional namespace test file

tests/namespace_test/namespace_test1_generated.lobster

@@ -3,6 +3,10 @@ import flatbuffers
 
 namespace NamespaceA_NamespaceB
 
+enum UnionInNestedNS:
+    UnionInNestedNS_NONE = 0
+    UnionInNestedNS_TableInNestedNS = 1
+
 enum EnumInNestedNS:
     EnumInNestedNS_A = 0
     EnumInNestedNS_B = 1