Follow-up to 12a4c08ad8.
I didn't review it carefully enough to notice that when these
functions return arrays, they contain a message key and parameters,
not a key and fallback keys (while other API documentation message
code uses fallback keys).
Instead of `$this->msg( $msg )`, this code must be written as
`is_array( $msg ) ? $this->msg( ...$msg ) : $this->msg( $msg )`
or `$this->msg( Message::newFromSpecifier( $msg ) )`, both of which
are ugly, but the latter looks a bit better to me.
Bonus changes:
* Add documentation to prevent a repeat of this mistake in the future
* Remove some unreachable dieDebug() calls (the Message class already
throws for bad inputs)
It seems that we don't have any definitions using such arrays
in the core API classes. There are only a few uses in extensions,
e.g. AbuseFilter's 'apihelp-query+abuselog-param-filter' message,
which is passed the wrong parameter without this change.
Bug: T372988
Change-Id: I44c1c3c7d0c069e500c85a58c27e9b675b0b68ee
0c0d50ce81