[llvm] [LV] Emit better debug and opt-report messages when vectorization is disallowed in the LoopVectorizer (PR #158513)

[Tibor Győri via llvm-commits]

TiborGY wrote:

> @TiborGY would you like me to commit this on your behalf (not sure if you have commit access).
> 
> If not just let me know, after taking a look at [#158513 (comment)](https://github.com/llvm/llvm-project/pull/158513#discussion_r2541267151)

Yes, please do, I don't have commit access. If you don't wish to wait any longer, feel free to commit whenever convenient.
Or next week after I have looked into [#158513 (comment)](https://github.com/llvm/llvm-project/pull/158513#discussion_r2541267151).

Thanks for the reviews and bearing with me through this long iteration process.

https://github.com/llvm/llvm-project/pull/158513