[clang] [Clang][Interp] Visit `DecompositionDecl` and create a local variable (PR #100400)

[Timm Baeder via cfe-commits]

https://github.com/tbaederr approved this pull request.

LGTM with the suggested changes. This might not be perfect wrt. revisiting `DecompositionDecl`s, but we can handle problems when they arise.

https://github.com/llvm/llvm-project/pull/100400