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

[Mainak Sil via cfe-commits]

MainakSil wrote:

I have addressed the feedback:
1. Removed unnecessary whitespace.
2. Removed redundant comments and the `FinalDerived` example.
3. Replaced `new/delete` with direct array passing.

Please let me know if further changes are needed.

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