not translating backend types for ps and log_line_prefix

Hello,

Pursuant to my comments in [1], I attach a patch that restricts the use
of translated process types as indicated in $SUBJECT. This adds a
separate column to the process type list, mostly extracted from Euler's
patch, not marked for translation, and uses it in a couple of places.
I think this is more reasonable. I chose to CC Heikki here because the
business with translating these strings was, as I recall, his doing ...

[1] https://postgr.es/m/202512091806.bsugq2l4wz7f@alvherre.pgsql

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Álvaro Herrera 48°01'N 7°57'E — https://www.EnterpriseDB.com/
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