[clang] [ItaniumMangle] Use mangleType instead of mangleNameOrStandardSubstitution in mangleCXXCtorVTable function (PR #109970)

[Richard Smith via cfe-commits]

zygoloid wrote:

> Do we need an ABI flag guarding against the change as well?

Yeah, I think this change should respect `-fclang-abi-compat`.

https://github.com/llvm/llvm-project/pull/109970