A named tuple type `(int mode, string label)` is a `tuple_type` whose
`tuple_element` children carry both a `type` and a `name` field.
_csharp_collect_type_refs walked every named child, so the element NAMES
were collected as type references, minted as sourceless placeholder nodes
and emitted `references` edges — one junk type node per element, repeated
in every file declaring such a signature.
Only the `type` field of each tuple element should feed type-reference
collection; the `name` is an identifier, not a type reference. Fix the
collector to descend into the element's type field only.
Regression: tests/test_csharp_tuple_type_refs.py asserts no node/edge is
minted for element names (all existing C# tests pass).
(cherry picked from commit bfcdda97b0)
KaiyiQuan
3c407dcb8c