fix(material-experimental/mdc-list): don't access class before initialization (#25049)
fix(material-experimental/mdc-list): don't access class before initialization (#25049)

Moves the `MatListBase` class up so that it isn't being referenced before it is used which seems to cause issues with Jest.

Fixes #25008.
angular/components,crisbeto/material2,crisbeto/material2,crisbeto/material2,crisbeto/material2,angular/components,angular/components,angular/components