[clang-tools-extra] [clang-tidy] Improve documentation of bugprone-pointer-arithmetic-on-polymorphic-object (PR #108324)

[via cfe-commits]

chrchr-github wrote:

Thank for addressing this.
I still wonder why using `new`/`delete` with additional UB (deleting pointer with offset) is necessary in the examples.
Why not simply define a function taking a pointer argument and do the arithmetic on that?

https://github.com/llvm/llvm-project/pull/108324