[clang] [clang] Track final substitution for Subst* AST nodes (PR #132748)

[Matheus Izvekov via cfe-commits]

mizvekov wrote:

@pranavk this test case is fixed by the same fix as for the first mangling issue: https://github.com/llvm/llvm-project/pull/135111

https://github.com/llvm/llvm-project/pull/132748