Add unified storage location setting

Currently only using it as a replacement for the downloads location.

(cherry picked from commit 695813ef7d922bc3d9ad5bccef8a466075caa57b)

core/src/main/java/tachiyomi/core/provider/AndroidStorageFolderProvider.kt

@@ -7,15 +7,14 @@ import tachiyomi.core.i18n.stringResource
 import tachiyomi.i18n.MR
 import java.io.File
 
-class AndroidDownloadFolderProvider(
-    val context: Context,
+class AndroidStorageFolderProvider(
+    private val context: Context,
 ) : FolderProvider {
 
     override fun directory(): File {
         return File(
             Environment.getExternalStorageDirectory().absolutePath + File.separator +
                 context.stringResource(MR.strings.app_name),
-            "downloads",
         )
     }