Implement posting threads (#6049)

* Implement posting a thread

Co-authored-by: Dan Abramov <dan.abramov@gmail.com>

* Fix native build

* Remove dependency on web crypto API

* Fix unrelated TS error (wtf)

---------

Co-authored-by: Mary <148872143+mary-ext@users.noreply.github.com>

src/view/com/composer/Composer.tsx

@@ -366,7 +366,7 @@ export const ComposePost = ({
             onStateChange: setPublishingStage,
             langs: toPostLanguages(langPrefs.postLanguage),
           })
-        ).uri
+        ).uris[0]
         try {
           await whenAppViewReady(agent, postUri, res => {
             const postedThread = res.data.thread