Add basic storage usage info to "Data and storage" settings screen

(cherry picked from commit cb8ea5eab0ec68ea02e8dc98c0a52771c460d5ab)

# Conflicts:
#	app/src/main/java/eu/kanade/presentation/more/settings/screen/SettingsDataScreen.kt

core/src/main/java/eu/kanade/tachiyomi/util/storage/DiskUtil.kt

@@ -28,6 +28,30 @@ object DiskUtil {
         return size
     }
 
+    /**
+     * Gets the total space for the disk that a file path points to, in bytes.
+     */
+    fun getTotalStorageSpace(file: File): Long {
+        return try {
+            val stat = StatFs(file.absolutePath)
+            stat.blockCountLong * stat.blockSizeLong
+        } catch (_: Exception) {
+            -1L
+        }
+    }
+
+    /**
+     * Gets the available space for the disk that a file path points to, in bytes.
+     */
+    fun getAvailableStorageSpace(file: File): Long {
+        return try {
+            val stat = StatFs(file.absolutePath)
+            stat.availableBlocksLong * stat.blockSizeLong
+        } catch (_: Exception) {
+            -1L
+        }
+    }
+
     /**
      * Gets the available space for the disk that a file path points to, in bytes.
      */

core/src/main/java/tachiyomi/core/preference/Preference.kt

@@ -35,7 +35,7 @@ interface Preference<T> {
 
         /**
          * A preference used for internal app state that isn't really a user preference
-         * and therefore should not be inplaces like backips.
+         * and therefore should not be in places like backups.
          */
         fun isAppState(key: String): Boolean {
             return key.startsWith(APP_STATE_PREFIX)