Change filename to username in toasts about sending thanks

This fixes #6466.

Also fix the messages themselves a bit:
* Removed "successfully" from the success message. This word
  is usually redundant, because the message already says that it
  was done. (In MediaWiki, there's a specific convention about it:
  https://www.mediawiki.org/wiki/Help:System_message#Avoid_jargon_and_slanghttps://www.mediawiki.org/wiki/Help:System_message#Avoid_jargon_and_slang
)
* Added a missing preposition to the failure message.

app/src/main/java/fr/free/nrw/commons/media/MediaDetailFragment.kt

@@ -1027,12 +1027,12 @@ class MediaDetailFragment : CommonsDaggerSupportFragment(), CategoryEditHelper.C
         val message: String = if (result) {
             context.getString(
                 R.string.send_thank_success_message,
-                media!!.displayTitle
+                media!!.user
             )
         } else {
             context.getString(
                 R.string.send_thank_failure_message,
-                media!!.displayTitle
+                media!!.user
             )
         }
 

app/src/main/res/values/strings.xml

@@ -494,8 +494,8 @@ Upload your first media by tapping on the add button.</string>
   <string name="check_category_toast">Requesting category check for %1$s</string>
   <string name="nominate_for_deletion_done">Done</string>
   <string name="send_thank_success_title">Sending Thanks: Success</string>
-  <string name="send_thank_success_message">Successfully sent thanks to %1$s</string>
-  <string name="send_thank_failure_message">Failed to send thanks %1$s</string>
+  <string name="send_thank_success_message">Sent thanks to %1$s</string>
+  <string name="send_thank_failure_message">Failed to send thanks to %1$s</string>
   <string name="send_thank_failure_title">Sending Thanks: Failure</string>
 
   <string name="send_thank_toast">Sending Thanks for %1$s</string>