* 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
* address changes
* add bone code for new isEqual and unit test for old isEqual
* add bone code for `FIRCollectionReference`, `FIRDocumentSnapshot`, `FIRFieldValue`, `FIRQuerySnapshot`, `FIRSnapshotMetadata`;
* change inconsistenciness of `FIRFieldPath.isEqual` implementation;
* add unit test (and file) for `FIRDocumentReferenceTest.m`, `FIRFieldPathTest.m`, `FIRQueryTests.testEquals`; `FIRGeoPoint` already has test and Blob is internal type.
* Implement isEqual for FIRCollectionReference
adding the working code and unit test.
* implement isEqual for FIRSnapshotMetadata
* Implement isEqual for FIRDocumentSnapshot
* Implement isEqual for FIRQuerySnapshot
* (un)implement `isEqual` for `FIRFieldValue`
Since `FIRFieldValue` both types are singleton, we do not need override `isEqual`. Add test to test the default `NSObject` `isEqual` works just fine.
* fix style with `scripts/style.sh`
* Implement hash for those with overridden isEqual without hash yet.
* refactor to use test helper functions -- FSTTestFirestore, FSTTestPath, FSTTestDocKey
* refactor using test helper `FSTTestDocSnapshot`, `FSTTestFieldPath`, `FSTTestQuery`, `FSTTestDoc`
* refactoring to use test helper method `FSTTestQuerySnapshot`,
* remove unneccessary nil-check, check isKindOfClass instead of isEqual
* refactoring: adding `FSTAPIHelpers.{h,m}`, `FSTTest{Collection,Document}Ref`, better naming and style fix
* a file forgot in last commit
* mainly clean up import and some minor refactoring
* fix style via style.sh
* minor style fix
* add pragma ignored -Wnonnull
zxu