[clang] [clang-tools-extra] First run at removing the linked-list for decls. Tests not run, but … (PR #113983)

[Erich Keane via cfe-commits]

erichkeane wrote:

This still crashes a lot locally, a few of my asserts are finding cases where a declaration is not in the list of decls of its parent for some reason.  I think there is value to do this, but it might have to be broken up.

https://github.com/llvm/llvm-project/pull/113983