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, 12 insertions, 8 deletions

diff --git a/Firestore/Source/Model/FSTDocumentSet.mm b/Firestore/Source/Model/FSTDocumentSet.mm
index 6f44799..2f0b42b 100644
--- a/Firestore/Source/Model/FSTDocumentSet.mm
+++ b/Firestore/Source/Model/FSTDocumentSet.mm
@@ -20,6 +20,10 @@
 #import "Firestore/Source/Model/FSTDocumentKey.h"
 #import "Firestore/third_party/Immutable/FSTImmutableSortedSet.h"
 
+#include "Firestore/core/src/firebase/firestore/model/document_key.h"
+
+using firebase::firestore::model::DocumentKey;
+
 NS_ASSUME_NONNULL_BEGIN
 
 /**
@@ -119,12 +123,12 @@ typedef FSTImmutableSortedSet<FSTDocument *> SetType;
   return [self.index isEmpty];
 }
 
-- (BOOL)containsKey:(FSTDocumentKey *)key {
-  return [self.index objectForKey:key] != nil;
+- (BOOL)containsKey:(const DocumentKey &)key {
+  return [self.index objectForKey:(FSTDocumentKey *)key] != nil;
 }
 
-- (FSTDocument *_Nullable)documentForKey:(FSTDocumentKey *)key {
-  return [self.index objectForKey:key];
+- (FSTDocument *_Nullable)documentForKey:(const DocumentKey &)key {
+  return [self.index objectForKey:(FSTDocumentKey *)key];
 }
 
 - (FSTDocument *_Nullable)firstDocument {
@@ -135,8 +139,8 @@ typedef FSTImmutableSortedSet<FSTDocument *> SetType;
   return [self.sortedSet lastObject];
 }
 
-- (NSUInteger)indexOfKey:(FSTDocumentKey *)key {
-  FSTDocument *doc = [self.index objectForKey:key];
+- (NSUInteger)indexOfKey:(const DocumentKey &)key {
+  FSTDocument *doc = [self.index objectForKey:(FSTDocumentKey *)key];
   return doc ? [self.sortedSet indexOfObject:doc] : NSNotFound;
 }
 
@@ -171,8 +175,8 @@ typedef FSTImmutableSortedSet<FSTDocument *> SetType;
   return [[FSTDocumentSet alloc] initWithIndex:index set:set];
 }
 
-- (instancetype)documentSetByRemovingKey:(FSTDocumentKey *)key {
-  FSTDocument *doc = [self.index objectForKey:key];
+- (instancetype)documentSetByRemovingKey:(const DocumentKey &)key {
+  FSTDocument *doc = [self.index objectForKey:(FSTDocumentKey *)key];
   if (!doc) {
     return self;
   }