Update CODEOWNERS to match recursively (#3650)
Update CODEOWNERS to match recursively (#3650)

Our CODEOWNERS file was not doing [recursive matching on directories which require `**` globs](https://git-scm.com/docs/gitattributes). We also failed to use the `@username` syntax [documented in the announcement](https://blog.github.com/2017-07-06-introducing-code-owners/).
randallli/material-components-ios,randallli/material-components-ios,randallli/material-components-ios,material-components/material-components-ios,randallli/material-components-ios,randallli/material-components-ios,material-components/material-components-ios,material-components/material-components-ios,randallli/material-components-ios,material-components/material-components-ios,material-components/material-components-ios