Add support for backing up wallpapers.

app/src/main/java/org/thoughtcrime/securesms/attachments/WallpaperAttachment.kt

@@ -0,0 +1,45 @@
+/*
+ * Copyright 2024 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.thoughtcrime.securesms.attachments
+
+import org.thoughtcrime.securesms.database.AttachmentTable
+import org.thoughtcrime.securesms.database.AttachmentTable.TransformProperties
+import org.thoughtcrime.securesms.util.MediaUtil
+
+/**
+ * A basically-empty [Attachment] that is solely used for inserting an attachment into the [AttachmentTable].
+ */
+class WallpaperAttachment() : Attachment(
+  contentType = MediaUtil.IMAGE_WEBP,
+  transferState = AttachmentTable.TRANSFER_PROGRESS_DONE,
+  size = 0,
+  fileName = null,
+  cdn = Cdn.CDN_0,
+  remoteLocation = null,
+  remoteKey = null,
+  remoteIv = null,
+  remoteDigest = null,
+  incrementalDigest = null,
+  fastPreflightId = null,
+  voiceNote = false,
+  borderless = false,
+  videoGif = false,
+  width = 0,
+  height = 0,
+  incrementalMacChunkSize = 0,
+  quote = false,
+  uploadTimestamp = 0,
+  caption = null,
+  stickerLocator = null,
+  blurHash = null,
+  audioHash = null,
+  transformProperties = TransformProperties.empty(),
+  uuid = null
+) {
+  override val uri = null
+  override val publicUri = null
+  override val thumbnailUri = null
+}