Make sure we clean up the pre-processed and uploaded media (#5039)

* Add `MediaSender.cleanUp()` and `MediaPreProcessor.cleanUp()` methods: this will remove the temporary files created when pre-processing media before sending them.

* Make sure we clean up also the previous temporary media.

* Fix the condition for the custom back handler in the attachments preview screen

* Tests: check the clean up is performed when needed

libraries/mediaupload/api/src/main/kotlin/io/element/android/libraries/mediaupload/api/MediaPreProcessor.kt

@@ -22,5 +22,10 @@ interface MediaPreProcessor {
         compressIfPossible: Boolean,
     ): Result<MediaUploadInfo>
 
+    /**
+     * Clean up any temporary files or resources used during the media processing.
+     */
+    fun cleanUp()
+
     data class Failure(override val cause: Throwable?) : Exception(cause)
 }

libraries/mediaupload/api/src/main/kotlin/io/element/android/libraries/mediaupload/api/MediaSender.kt

@@ -200,4 +200,9 @@ class MediaSender @Inject constructor(
                 uploadHandler.await()
             }
     }
+
+    /**
+     * Clean up any temporary files or resources used during the media processing.
+     */
+    fun cleanUp() = preProcessor.cleanUp()
 }