* lint.sh now lints Objective-C++ too
* cpplint checks system-style includes that should be user-style
This prevents it from recognizing project sources as if they were C
system headers and then complaining that they're in the wrong place.
* cpplint checks #imports and #includes
* cpplint checks that C++ system headers aren't #imported
* cpplint checks for C system headers that could be C++ system headers
* cpplint checks that Objective-C sources include their headers
This simplifies the import process back into google3 and allows us to add additional directories to the project without needing to update the project files for each directory we add. This shows up most clearly in the change to Firestore/Example/Firestore.xcodeproj/project.pbxproj: this no longer needs to list essentially every directory in the project as a header search path.
* Clang-format configuration for C++ files
* Add support C++-only sources to the podspec
* Podspec support for fully qualified imports
* xcodeproj changes for fully-qualified imports
* Use fully-qualified imports in Firestore sources