Add language dropdown to compose view (#2651)

* Add UI for selecting post language

* Apply selected language when sending status

* Save/restore post language with drafts

* Fall back to english if the configured language isn't found in the locale list (no-NB)

* Remove comment about no_NB

* Move language dropdown to top of compose view

* Preserve language when redrafting

* Set default language to target post's language when replying

* Add Tusky license header to new source file

* Tweak language dropdown button width

app/src/test/java/com/keylesspalace/tusky/components/timeline/StatusMocker.kt

@@ -51,7 +51,8 @@ fun mockStatus(
     pinned = false,
     muted = false,
     poll = null,
-    card = null
+    card = null,
+    language = null,
 )
 
 fun mockStatusViewData(