* Move the util::objc namespace to just objc
This removes all the namespace objc = firebase::firestore::util::objc
gunk to make it seem as if this was really the arrangement.
This is motivated by wanting to put additional things in this namespace
and use them in headers without having to use util::objc::Foo
* Add CMake support for header-only cc_library targets
* Have the linter allow #include <objc/objc.h>, a C header
* Define a Comparator for DocumentKey
* Automated migration from FSTDocumentKeySet to DocumentKeySet
* Manual fixups for DocumentKeySet
* Delete FSTDocumentKeySet
* remove conversions in `Local` and `Remote`
* replace `FSTSnapshotVersion` in `Model`
* replace `FSTSnapshotVersion` in the rest
* let test check equal with C++ equal
* fix newly added code
* address changes
* 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
- FSTTimestamp is now FIRTimestamp, under Firestore/Source/{Public,API}. This is a temporary solution; eventually, FIRTimestamp is supposed to live somewhere under Firebase;
- move most internal Timestamp methods to the public header (the only exception is ISOString).
* Move all Firestore files to Objective-C++
* Update project file references
* Don't use module imports from Objective-C++
* Use extern "C" for C-accessible globals
* Work around more stringent type checking in Objective-C++
* NSMutableDictionary ivars aren't implicitly casted to NSDictionary
* FSTMaybeDocument callback can't be passed a function that accepts
FSTDocument
* NSComparisonResult can't be multiplied by -1 without casting
* Add a #include <inttypes.h> where needed
* Avoid using C++ keywords as variables
* Remove #if __cplusplus guards
Gil