compose: Paste content into the compose box without adding any space.

We replace the call to `insert_syntax_and_focus` with a direct call to
`insert_and_scroll_into_view` when pasting content into the compose box,
which fixes the bug where leading and trailing spaces were added to any
pasted content.

web/src/copy_and_paste.js

@@ -547,7 +547,7 @@ export function paste_handler(event) {
             event.preventDefault();
             event.stopPropagation();
             const text = paste_handler_converter(paste_html);
-            compose_ui.insert_syntax_and_focus(text, $textarea);
+            compose_ui.insert_and_scroll_into_view(text, $textarea);
         }
     }
 }