Update `str*time` to C11 format codes

Feature or enhancement

There are several things to do, these are already supported by strftime but some (support for a few was added recently but not documented) are not supported by strptime (e.g. %t is not supported).

• Update docs, currently the table is a bit messy with non-standard format codes listed, i.e. %f, and quite a few codes are missing.
• Refactor strftime tests, they were written when the format codes were not expected.
• Complete strptime, e.g. %n.
• Document that strptime collapses whitespace, %t an %n
• Consider: Add an entry to What's New

I will be working on this and most likely extending this list.

Linked PRs

• gh-140716
• gh-140647
• gh-123980
• gh-144819
• gh-144896
• gh-145388
• gh-145389
• gh-145955