[diff] Reorder Annex C entries to respect clause numbering

[Mick235711]

After clause renumbering efforts in C++23 and C++26, currently [strings] is Clause 27, which makes the Annex C entries unordered in relation to actual clause numbers (for instance, under [diff.cpp20], [diff.cpp20.strings] refers to Clause 27, while [diff.cpp20.containers] refers to Clause 23; however, the former comes first). Therefore, this PR seeks to correct the situation by reordering the entries with regard to current clause numbers:

• Swap the positions of [diff.cpp20.strings] and [diff.cpp20.containers]
• Swap the positions of [diff.cpp14.strings] and [diff.cpp14.containers]
• Move [diff.cpp03.strings] after [diff.cpp03.algorithms]
• [diff.cpp03.locale] is currently the only Annex C entry that does not refer to a whole clause, making its title "28.3: localization library" which is inconsistent with everything else. This PR thus makes it refer to Clause 28 (text processing library) instead, and moves it before [diff.cpp03.numerics] to maintain the numerical ordering
  • It seems inappropriate to change the stable labels for this; there have been precedents for [diff.cppXX.foo] not referring to [foo] before (e.g. [diff.cpp23.io], [diff.stat])

[jensmaurer]

I'm generally in favor here. However, as usual with such large text rearrangements, it's hard to review them ("did the submitter change a character or two while moving the text around?") This is not about bad faith, but about accidents.

@tkoeppe , do you want to apply as-is, do the moves yourself, or have me do the moves?

[tkoeppe]

@jensmaurer If you want to do it all in one go and merge, yes, please go ahead, that'd be nice!