android.support.v4.content.FileProvider not found

As of AndroidX (the repackaged Android Support Library), the path is androidx.core.content.FileProvider so the updated provider tag would be:

<provider
    android:name="androidx.core.content.FileProvider"
    android:authorities="${applicationId}.fileprovider"
    android:exported="false"
    android:grantUriPermissions="true">
    <meta-data
        android:name="android.support.FILE_PROVIDER_PATHS"
        android:resource="@xml/file_paths" />
</provider>

Android Support Libraries are now in the androidx.* package hierarchy.

android.* is now reserved to the built-in Android System Libraries.