tree-wide: avoid some loaded terms

https://tools.ietf.org/html/draft-knodel-terminology-02
https://lwn.net/Articles/823224/

This gets rid of most but not occasions of these loaded terms:

1. scsi_id and friends are something that is supposed to be removed from
   our tree (see #7594)

2. The test suite defines an API used by the ubuntu CI. We can remove
   this too later, but this needs to be done in sync with the ubuntu CI.

3. In some cases the terms are part of APIs we call or where we expose
   concepts the kernel names the way it names them. (In particular all
   remaining uses of the word "slave" in our codebase are like this,
   it's used by the POSIX PTY layer, by the network subsystem, the mount
   API and the block device subsystem). Getting rid of the term in these
   contexts would mean doing some major fixes of the kernel ABI first.

Regarding the replacements: when whitelist/blacklist is used as noun we
replace with with allow list/deny list, and when used as verb with
allow-list/deny-list.

docs/USER_NAMES.md

@@ -68,9 +68,9 @@ Distilled from the above, below are the rules systemd enforces on user/group
 names. An additional, common rule between both modes listed below is that empty
 strings are not valid user/group names.
 
-Philosophically, the strict mode described below enforces a white-list of what's
-allowed and prohibits everything else, while the relaxed mode described below
-implements a blacklist of what's not allowed and permits everything else.
+Philosophically, the strict mode described below enforces an allow list of
+what's allowed and prohibits everything else, while the relaxed mode described
+below implements a deny list of what's not allowed and permits everything else.
 
 ### Strict mode