Port FSTFirestoreClient to C++ 2/2 (#3657)

* firestore_client + FSTFirestoreClient becomes delegate.

* fix comment

* addressing comment

* use new instead make_shared

* reformat

* Update references to firestore client

* Addressing comments#2

* addressing comments #3

* add std::move

* remove deleted header.

* fix cmake build error.

Author: wu-hui

Firestore/Example/Tests/Integration/API/FIRDatabaseTests.mm

@@ -22,7 +22,8 @@
 #import "Firestore/Example/Tests/Util/FSTEventAccumulator.h"
 #import "Firestore/Example/Tests/Util/FSTIntegrationTestCase.h"
 #import "Firestore/Source/API/FIRFirestore+Internal.h"
-#import "Firestore/Source/Core/FSTFirestoreClient.h"
+
+#include "Firestore/core/src/firebase/firestore/core/firestore_client.h"
 #include "Firestore/core/test/firebase/firestore/testutil/app_testing.h"
 
 namespace testutil = firebase::firestore::testutil;
@@ -1354,8 +1355,7 @@ - (void)testAppDeleteLeadsToFirestoreShutdown {
 
   [self deleteApp:app];
 
-  FSTFirestoreClient *client = firestore.wrapped->client();
-  XCTAssertTrue([client isShutdown]);
+  XCTAssertTrue(firestore.wrapped->client()->is_shutdown());
 }
 
 - (void)testShutdownCanBeCalledMultipleTimes {

Firestore/Example/Tests/Integration/FSTTransactionTests.mm

@@ -21,7 +21,6 @@
 
 #import "Firestore/Example/Tests/Util/FSTIntegrationTestCase.h"
 #import "Firestore/Source/API/FIRFirestore+Internal.h"
-#import "Firestore/Source/Core/FSTFirestoreClient.h"
 #import "Firestore/Source/Util/FSTClasses.h"
 
 using firebase::firestore::util::TimerId;

Firestore/Source/API/FIRQuery.mm

@@ -33,13 +33,13 @@
 #import "Firestore/Source/API/FIRQuerySnapshot+Internal.h"
 #import "Firestore/Source/API/FIRSnapshotMetadata+Internal.h"
 #import "Firestore/Source/API/FSTUserDataConverter.h"
-#import "Firestore/Source/Core/FSTFirestoreClient.h"
 
 #include "Firestore/core/src/firebase/firestore/api/input_validation.h"
 #include "Firestore/core/src/firebase/firestore/api/query_core.h"
 #include "Firestore/core/src/firebase/firestore/core/bound.h"
 #include "Firestore/core/src/firebase/firestore/core/direction.h"
 #include "Firestore/core/src/firebase/firestore/core/filter.h"
+#include "Firestore/core/src/firebase/firestore/core/firestore_client.h"
 #include "Firestore/core/src/firebase/firestore/core/order_by.h"
 #include "Firestore/core/src/firebase/firestore/core/query.h"
 #include "Firestore/core/src/firebase/firestore/model/document_key.h"
@@ -178,11 +178,11 @@ - (void)getDocumentsWithSource:(FIRFirestoreSource)publicSource
       });
 
   // Call the view_listener on the user Executor.
-  auto async_listener = AsyncEventListener<ViewSnapshot>::Create(firestore->client().userExecutor,
-                                                                 std::move(view_listener));
+  auto async_listener = AsyncEventListener<ViewSnapshot>::Create(
+      firestore->client()->user_executor(), std::move(view_listener));
 
   std::shared_ptr<QueryListener> query_listener =
-      [firestore->client() listenToQuery:query options:internalOptions listener:async_listener];
+      firestore->client()->ListenToQuery(query, internalOptions, async_listener);
 
   return [[FSTListenerRegistration alloc]
       initWithRegistration:ListenerRegistration(firestore->client(), std::move(async_listener),