src/: Rename the various `:lisp-class' properties.

src/: Rename the various `:lisp-class' properties.

Instead, there's now a separate property for each kind of metaobject.
The reason is that some declarations can produce two metaobjects, e.g.,
a message declaration might also include a direct method, and we can't
possibly use the same metaobject class for both.  To resolve this, we
use different properties to name the different metaobject classes.

  * For classes, we use `:lisp-metaclass' (to distinguish from a runtime
    metaclass).

  * For messages, `:message-class'.

  * For methods, `:method-class'.

  * For slots, `:slot-class'.

  * For slot initializers, `:initializer-class'.

  * For modules, `:module-class'.