Another step toward switching to std::format notation.

The basic strategy is to make sure that all the classes that have
errorf (etc) methods using printf notation will also have errorfmt
(etc) methods using std::format notation. These will coexist for a
while to let people switch, before the printf ones will be marked
deprecated and then eventually removed.

In some cases where the methods aren't really part of the public
API, but only are used internally, we are already skipping to the
deprecation marking.

Signed-off-by: Larry Gritz <lg@larrygritz.com>

Signed-off-by: Larry Gritz <lg@larrygritz.com>