Extend Signal subdirectory organization to all media types

Now all media types are organized in Signal subdirectories
- Images: Pictures/Signal/
- Videos: Movies/Signal/
- Audio: Music/Signal/
- Documents: Documents/Signal/ (Android 9-) or Download/Signal/ (Android 10+)

Note: Documents vs Downloads difference for generic files
existed before this change - this PR only adds Signal
subdirectory organization.

Author: Verryx-02

app/src/main/java/org/thoughtcrime/securesms/util/SaveAttachmentUtil.kt

@@ -156,8 +156,14 @@ object SaveAttachmentUtil {
       MediaStore.MediaColumns.DATE_MODIFIED to TimeUnit.MILLISECONDS.toSeconds(System.currentTimeMillis())
     )
 
-    if (Build.VERSION.SDK_INT > 28 && contentType.startsWith("image/")) {
-      contentValues.put(MediaStore.MediaColumns.RELATIVE_PATH, Environment.DIRECTORY_PICTURES + "/Signal")
+    if (Build.VERSION.SDK_INT > 28) {
+      val relativePath = when {
+        contentType.startsWith("image/") -> Environment.DIRECTORY_PICTURES + "/Signal"
+        contentType.startsWith("video/") -> Environment.DIRECTORY_MOVIES + "/Signal"
+        contentType.startsWith("audio/") -> Environment.DIRECTORY_MUSIC + "/Signal"
+        else -> Environment.DIRECTORY_DOWNLOADS + "/Signal"
+      }
+      contentValues.put(MediaStore.MediaColumns.RELATIVE_PATH, relativePath)
     }
 
     if (Build.VERSION.SDK_INT > 28) {
@@ -217,10 +223,10 @@ object SaveAttachmentUtil {
 
   private fun getExternalPathForType(contentType: String): String? {
     val storage: File? = when {
-      contentType.startsWith("video/") -> Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_MOVIES)
-      contentType.startsWith("audio/") -> Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_MUSIC)
+      contentType.startsWith("video/") -> File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_MOVIES), "Signal")
+      contentType.startsWith("audio/") -> File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_MUSIC), "Signal")
       contentType.startsWith("image/") -> File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES), "Signal")
-      else -> Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOCUMENTS)
+      else -> File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS), "Signal")
     }
 
     return storage?.let { ensureExternalPath(storage) }?.absolutePath