Abstract useEmailSelection into separate function

src/composition/useEmailSelection.js

@@ -0,0 +1,19 @@
+import { ref } from 'vue';
+
+export const useEmailSelection = function(){
+  let selectedEmailIds = ref(new Set(['1', '5']))
+  let toggleEmailSelection = (id) => {
+    if(selectedEmailIds.value.has(id)) {
+      selectedEmailIds.value.delete(id)
+    } else {
+      selectedEmailIds.value.add(id);
+    }
+  }
+
+  return {
+    selectedEmailIds,
+    toggleEmailSelection
+  }
+}
+
+export default useEmailSelection;