[clang] [llvm] [clang][CodeGen] Generate follow-up metadata for loops in correct format (PR #131985)

[Ryotaro Kasuga via llvm-commits]

https://github.com/kasuga-fj commented:

>  Possibly the `create*Metadata` should only return a list of properties instead of an MDNode, with the MDNode only to be created when applying the properties to a Loop. However, the easier fix would probably be to extract the properties from the MDNode and append to the `followup_*` MDNode, with the returned MDNode becoming garbage-collected at some point.

Fixed `create*Metadata` to return a list of properties instead of an MDNode. I believe unnecessary MDNodes would not be generated.

https://github.com/llvm/llvm-project/pull/131985