[clang] [Clang][AST] Move NamespaceDecl bits to DeclContext (PR #98567)

[Vlad Serebrennikov via cfe-commits]

Endilll wrote:

Worth noting I've been investigating in the background whether we can do the opposite transformation, i.e. move members of `*Bits` back to their respective classes without increasing size of AST nodes. If anything, for the sake of debugging experience. The prototype is here: https://godbolt.org/z/4b7Gv9Eb8, but there's still some work to do before the deployment, because it uncovered false-positives in our diagnostics.

https://github.com/llvm/llvm-project/pull/98567