[Switch] Document the use of UISwitch (#4714)
[Switch] Document the use of UISwitch (#4714)

iOS does not implement Material Switches because the iOS native UISwitch should be used instead. This is captured in the cross-platform adaptation guidelines.

Closes #3862

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