port `DocumentKey` to non-container types of `Model/*` (#930)

* naively remove FSTPath import and source/test files.

* port FieldPath, part I

* port FieldPath, part II

* port ResourcePath, part I

* port ResourcePath, part II

* the grand commit to fix build errors

* use testutil:: helper instead of those from FSTHelpers

* fix test and lint

* use c_str in errmsg directly

* fix

* fix

* make code clean

* fix integration test I missed

* fix to avoid naming collision in preprocessor

* address changes

* address changes

* address changes

* fix: fieldMask are actually shared with different context.

* address changes

* add converter function between two DocumentKey implementations

* add unit test

* address changes

* fix lint

* using DocumentKey in model except for the container types `FSTDocumentDictionary`, `FSTDocumentKeySet`, and  `FSTDocumentVersionDictionary`

* change other place w.r.t. the use of `DocumentKey` in model

* update parameter of test helpers from NSString to string_view

* revert a temporary change used in debug

* address changes

1 files changed, 8 insertions, 3 deletions

diff --git a/Firestore/Source/Model/FSTMutationBatch.mm b/Firestore/Source/Model/FSTMutationBatch.mm
index 07aadbb..6598d27 100644
--- a/Firestore/Source/Model/FSTMutationBatch.mm
+++ b/Firestore/Source/Model/FSTMutationBatch.mm
@@ -24,6 +24,10 @@
 #import "Firestore/Source/Model/FSTMutation.h"
 #import "Firestore/Source/Util/FSTAssert.h"
 
+#include "Firestore/core/src/firebase/firestore/model/document_key.h"
+
+using firebase::firestore::model::DocumentKey;
+
 NS_ASSUME_NONNULL_BEGIN
 
 const FSTBatchID kFSTBatchIDUnknown = -1;
@@ -68,10 +72,11 @@ const FSTBatchID kFSTBatchIDUnknown = -1;
 }
 
 - (FSTMaybeDocument *_Nullable)applyTo:(FSTMaybeDocument *_Nullable)maybeDoc
-                           documentKey:(FSTDocumentKey *)documentKey
+                           documentKey:(const DocumentKey &)documentKey
                    mutationBatchResult:(FSTMutationBatchResult *_Nullable)mutationBatchResult {
   FSTAssert(!maybeDoc || [maybeDoc.key isEqualToKey:documentKey],
-            @"applyTo: key %@ doesn't match maybeDoc key %@", documentKey, maybeDoc.key);
+            @"applyTo: key %s doesn't match maybeDoc key %s", documentKey.ToString().c_str(),
+            maybeDoc.key.ToString().c_str());
   FSTMaybeDocument *baseDoc = maybeDoc;
   if (mutationBatchResult) {
     FSTAssert(mutationBatchResult.mutationResults.count == self.mutations.count,
@@ -94,7 +99,7 @@ const FSTBatchID kFSTBatchIDUnknown = -1;
 }
 
 - (FSTMaybeDocument *_Nullable)applyTo:(FSTMaybeDocument *_Nullable)maybeDoc
-                           documentKey:(FSTDocumentKey *)documentKey {
+                           documentKey:(const DocumentKey &)documentKey {
   return [self applyTo:maybeDoc documentKey:documentKey mutationBatchResult:nil];
 }