fix(material-experimental/mdc-button): align public API with material/button (#20679)
fix(material-experimental/mdc-button): align public API with material/button (#20679)

Aligns the signature of the `focus` method between the MDC and non-MDC buttons to make updates easier.
andrewseguin/material2,crisbeto/material2,josephperrott/material2,DevVersion/material2,mmalerba/material2,andrewseguin/material2,crisbeto/material2,josephperrott/material2,DevVersion/material2,angular/components,andrewseguin/material2,josephperrott/material2,mmalerba/material2,DevVersion/material2,angular/components,mmalerba/material2,mmalerba/material2,angular/components,DevVersion/material2,crisbeto/material2,DevVersion/material2,josephperrott/material2,andrewseguin/material2,andrewseguin/material2,mmalerba/material2,angular/components,crisbeto/material2,josephperrott/material2