* Manual Xcode project fixups
* Remove `firebase/firestore` from paths in Firestore/core
This renames all Firestore files under `Firestore/core` to remove the
interior `firebase/firestore` directory structure. This is motivated by
build failures under Windows where the filenames of intermediates were
too long.
Concretely:
* `Firebase/core/src/firebase/firestore` becomes `Firebase/core/src`
* `Firebase/core/test/firebase/firestore` becomes
`Firebase/core/test/unit`
Moving the tests into a `unit` subdirectory aligns Firestore with the
directory structure in
[AddNewPod](https://github.com/firebase/firebase-ios-sdk/blob/master/AddNewPod.md),
modified for C++ (see discussion in #3224).
* Remove rarely used template argumnets from SortedMap/SortedSet
* Remove unused STATUS_CHECK_OK
* Rename QuerySnapshot::Listener to QuerySnapshotListener
This makes the type something that can be forward declared.
* Rename DocumentSnapshot::Listener to DocumentSnapshotListener
This makes the type something that can be forward declared.
* Rename ViewSnapshot::Listener to ViewSnapshotListener
This makes the type something that can be forward declared.
* Put most QueryListener implementation in .cc
* Actually use sync_engine_callback.h
* Add forward declaration headers for api, core, and model
These centralize forward declarations, including declarations for some
hard-to-forward-declare types.
* Move includes of hard_assert.h out of other headers
* Make testutil definitions out of line
* Move definitions out-of-line
* Move DocumentKey definitions out-of-line
* Move definitions out-of-line
* Shorten unnecessarily long namespace usages
* Use default destructors where possible
* Delete unused MutationBatch::kUnknown constant
* Use forward declarations instead of IWYU
* Misc fixups from Linux/GCC 9.2.1
* Fix testutil under VS 2017
Forward declarations of functions local to a function body end up
generating unresolved externals. Reduce most of these back to just
calling FieldValue::FromX methods.
* 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
* 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
Denver Coneybeare