[Availability] Add an umbrella header.
[Availability] Add an umbrella header.

All components are expected, by convention, to have an umbrella header.

PiperOrigin-RevId: 293804134

material-components/material-components-ios,material-components/material-components-ios,material-components/material-components-ios,material-components/material-components-ios,material-components/material-components-ios