gh-140715: Add `%D` format code support to `strptime()` (GH-144819)

* %D support for strptime, including test and Doc update
* additional %D test
* change documentation example date for %D so it is more legible to non-US readers
* change testing date for %D so it is more legible to non-US readers
* mv News blurb to Library, consistent with previous %F change
* change invalid format code from %D to C-standard unused %!
* Fix erroneous and misleading example Doc to %y from %Y, use correct C99+ definition for C99 %D; update additional tests

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Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>