The last remaining ERR_EXPLAIN call is in FreeType code and makes sense as is
(conditionally defines the error message).
There are a few ERR_EXPLAINC calls for C-strings where String is not included
which can stay as is to avoid adding additional _MSGC macros just for that.
Part of #31244.
Both client and server are supported on native builds (as usual).
SSL server is still not supported, but will soon be possible with this
new library.
The API stays the same, we just need to work out potential issues due to
this big library switch.
