docs(material/dialog): state when notification observables close (#21336)
docs(material/dialog): state when notification observables close (#21336)

* docs(material/dialog): state when notification observables close

* docs(material/dialog): improve wording
andrewseguin/material2,mmalerba/material2,andrewseguin/material2,josephperrott/material2,andrewseguin/material2,angular/components,josephperrott/material2,andrewseguin/material2,DevVersion/material2,angular/components,DevVersion/material2,DevVersion/material2,mmalerba/material2,andrewseguin/material2,mmalerba/material2,josephperrott/material2,angular/components,crisbeto/material2,crisbeto/material2,crisbeto/material2,DevVersion/material2,crisbeto/material2,josephperrott/material2,josephperrott/material2,mmalerba/material2,mmalerba/material2,DevVersion/material2,angular/components