Re: Windows default locale vs initdb

Ertan Küçükoglu offered to try to review and test this, so here's a rebase.

Some notes:

* it turned out that the Turkish i/I test problem I mentioned earlier
in this thread[1] was just always broken on Windows, we just didn't
ever test with UTF-8 before Meson took over; it's skipped now, see
commit cff4e5a3[2]

* it seems that you can't actually put encodings like .1252 on the end
(.UTF-8 must be a special case); I don't know if we should look into a
better UTF-8 mode for modern Windows, but that'd be a separate project

* this patch only benefits people who run initdb.exe without
explicitly specifying a locale; probably a good number of real systems
in the wild actually use EDB's graphical installer which initialises a
cluster and has its own way of choosing the locale, as discussed in
Ertan's thread[3]

[1] https://www.postgresql.org/message-id/flat/CA%2BhUKGJZskvCh%3DQm75UkHrY6c1QZUuC92Po9rponj1BbLmcMEA%40mail.gmail.com#3a00c08214a4285d2f3c4297b0ac2be2
[2] https://github.com/postgres/postgres/commit/cff4e5a3
[3] https://www.postgresql.org/message-id/flat/CAH2i4ydECHZPxEBB7gtRG3vROv7a0d3tqAFXzcJWQ9hRsc1znQ%40mail.gmail.com