[client-app] Reindex threads when they're updated

This commit is the same as 7d409f5.

This commit was accidentally reverted in 95ec679, because I (juan) was being
dumb. So I'm re-committing here.

Summary:
We weren't doing that, so we would have accurate search index info for
threads when they were, e.g., moved to another folder.

Test Plan: Run locally

Reviewers: spang, evan, juan

Reviewed By: evan, juan

Differential Revision: https://phab.nylas.com/D4260

packages/client-app/internal_packages/search-index/lib/thread-search-index-store.es6

@@ -122,12 +122,21 @@ class ThreadSearchIndexStore {
     if (change.objectClass !== Thread.name) {
       return;
     }
-    _.defer(() => {
+    _.defer(async () => {
       const {objects, type} = change
       const threads = objects;
 
       let promises = []
       if (type === 'persist') {
+        const alreadyIndexedThreads = threads.filter(t => t.isSearchIndexed)
+        if (alreadyIndexedThreads.length > 0) {
+          alreadyIndexedThreads.forEach(thread => {
+            // Mark already indexed threads as unindexed so that we re-index them
+            // with updates
+            thread.isSearchIndexed = false
+          })
+          await DatabaseStore.inTransaction(t => t.persistModels(alreadyIndexedThreads))
+        }
         this.indexer.notifyHasIndexingToDo();
       } else if (type === 'unpersist') {
         promises = threads.map(thread => this.unindexThread(thread,