[over.ics.list] expand example 5, fix inconsistent spacing

[Eisenwave]

This edit expands the example to include the edge case where the std::initializer_list constructors competes with the copy constructor. This edge case has been the subject of some core issues:

• https://cplusplus.github.io/CWG/issues/1467.html
• https://cplusplus.github.io/CWG/issues/2137.html

It's also responsible for an LLVM bug where the copy constructor wins in overload resolution, and this is actively being worked on:

• Clang choosing copy constructor over initializer_list llvm/llvm-project#58520 (duplicate of)
• Single-element initializer_list invokes wrong constructor llvm/llvm-project#24186

To raise awareness for this issue, and how the edge case should be handled, it would be wise to include it in the example.

Furthermore, this edit fixes inconsistent comma spacing towards the beginning of the example. While the style is up to the author of the examples, they should at least follow consistent style, and not space 1,2,3 in one place, but 1.0, 2.0 in another.

[jensmaurer]

The spacing fix is fine. I'm not comfortable adding the example editorially.