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, 17 insertions, 16 deletions

diff --git a/Firestore/Example/Tests/API/FSTAPIHelpers.mm b/Firestore/Example/Tests/API/FSTAPIHelpers.mm
index c180dc4..1ccf22e 100644
--- a/Firestore/Example/Tests/API/FSTAPIHelpers.mm
+++ b/Firestore/Example/Tests/API/FSTAPIHelpers.mm
@@ -58,14 +58,14 @@ FIRFirestore *FSTTestFirestore() {
   return sharedInstance;
 }
 
-FIRDocumentSnapshot *FSTTestDocSnapshot(NSString *path,
+FIRDocumentSnapshot *FSTTestDocSnapshot(const absl::string_view path,
                                         FSTTestSnapshotVersion version,
                                         NSDictionary<NSString *, id> *_Nullable data,
                                         BOOL hasMutations,
                                         BOOL fromCache) {
   FSTDocument *doc = data ? FSTTestDoc(path, version, data, hasMutations) : nil;
   return [FIRDocumentSnapshot snapshotWithFirestore:FSTTestFirestore()
-                                        documentKey:FSTTestDocKey(path)
+                                        documentKey:testutil::Key(path)
                                            document:doc
                                           fromCache:fromCache];
 }
@@ -82,7 +82,7 @@ FIRDocumentReference *FSTTestDocRef(const absl::string_view path) {
 
 /** A convenience method for creating a query snapshots for tests. */
 FIRQuerySnapshot *FSTTestQuerySnapshot(
-    NSString *path,
+    const absl::string_view path,
     NSDictionary<NSString *, NSDictionary<NSString *, id> *> *oldDocs,
     NSDictionary<NSString *, NSDictionary<NSString *, id> *> *docsToAdd,
     BOOL hasPendingWrites,
@@ -92,30 +92,31 @@ FIRQuerySnapshot *FSTTestQuerySnapshot(
   FSTDocumentSet *oldDocuments = FSTTestDocSet(FSTDocumentComparatorByKey, @[]);
   for (NSString *key in oldDocs) {
     oldDocuments = [oldDocuments
-        documentSetByAddingDocument:FSTTestDoc([NSString stringWithFormat:@"%@/%@", path, key], 1,
-                                               oldDocs[key], hasPendingWrites)];
+        documentSetByAddingDocument:FSTTestDoc(util::MakeStringView([NSString
+                                                   stringWithFormat:@"%s/%@", path.data(), key]),
+                                               1, oldDocs[key], hasPendingWrites)];
   }
   FSTDocumentSet *newDocuments = oldDocuments;
   NSArray<FSTDocumentViewChange *> *documentChanges = [NSArray array];
   for (NSString *key in docsToAdd) {
-    FSTDocument *docToAdd = FSTTestDoc([NSString stringWithFormat:@"%@/%@", path, key], 1,
-                                       docsToAdd[key], hasPendingWrites);
+    FSTDocument *docToAdd =
+        FSTTestDoc(util::MakeStringView([NSString stringWithFormat:@"%s/%@", path.data(), key]), 1,
+                   docsToAdd[key], hasPendingWrites);
     newDocuments = [newDocuments documentSetByAddingDocument:docToAdd];
     documentChanges = [documentChanges
         arrayByAddingObject:[FSTDocumentViewChange
                                 changeWithDocument:docToAdd
                                               type:FSTDocumentViewChangeTypeAdded]];
   }
-  FSTViewSnapshot *viewSnapshot =
-      [[FSTViewSnapshot alloc] initWithQuery:FSTTestQuery(util::MakeStringView(path))
-                                   documents:newDocuments
-                                oldDocuments:oldDocuments
-                             documentChanges:documentChanges
-                                   fromCache:fromCache
-                            hasPendingWrites:hasPendingWrites
-                            syncStateChanged:YES];
+  FSTViewSnapshot *viewSnapshot = [[FSTViewSnapshot alloc] initWithQuery:FSTTestQuery(path)
+                                                               documents:newDocuments
+                                                            oldDocuments:oldDocuments
+                                                         documentChanges:documentChanges
+                                                               fromCache:fromCache
+                                                        hasPendingWrites:hasPendingWrites
+                                                        syncStateChanged:YES];
   return [FIRQuerySnapshot snapshotWithFirestore:FSTTestFirestore()
-                                   originalQuery:FSTTestQuery(util::MakeStringView(path))
+                                   originalQuery:FSTTestQuery(path)
                                         snapshot:viewSnapshot
                                         metadata:metadata];
 }