use namespace aliases instead.
This makes the Objective-C code much more like what it's going to end up
being like when translated to C++: headers will include classes declared
in a namespace relative to firebase::firestore so everything else will
be named relative to firebase::firestore.
Meanwhile the using statements in the headers were causing us to miss
adding using statements in source files which was moving us away from
where we wanted to be.
* Create C++ api::DocumentChange class.
* Make FIRDocumentChange a wrapper over api::DocumentChange.
* Moved documentChangesForSnapshot helper from FIRDocumentChange to
where it's used in QuerySnapshot. I think this is cleaner.
* Replace `QueryListenOptions` with simple booleans
Instead of calling
addSnapshotListener(
options:QueryListenOptions.includeQueryMetadataChanges()
.includeDocumentMetadataChanges())
call
addSnapshotListener(includeMetadataChanges:true)
Also change `QuerySnapshot.documentChanges()` into a method which
optionally takes `includeMetadataChanges:true`. By default even when
listening to a query with `inlcudeMetadataChanges:true` metadata-only
document changes are suppressed because they're confusing.
* Revert QuerySnapshot.documentChanges back to a property
Add usage.
Gil