[ISO/CS C++2023] Fix punctuation details

[jensmaurer]

• 4.3 Syntax notation replace the full stops at the end of these list items with commas
• 5.13.8 User-defined literals add full stops after the "operator ""X (n ULL)" if it is the end of the sentence. This comment applies to this whole clause.
• 9.4.5 List-initialization all full stop at the end of the note.
• 30.4.3.2.3 Virtual functions add fullstop
• 30.4.3.2.3 Virtual functions add full stop

[jensmaurer]

Reject 4.3; those are complete sentences.
Reject 5.13.8; we can't plausibly add a period after a quote of C++ source code (the period might be mistaken as part of the C++ source code)

[tkoeppe]

For 5.13.8 we need a good explanation, but indeed, we definitely can't add any punctuation there.