firebase-ios-sdk

Build all sources with CMake (#4159)

* Fix field initialization order

* Reduce dependencies in objc_compatibility_apple_test

This makes it possible to build and test util without having to build
everything

* Add a lint check for CMake files

* Find XCTest, if available

* Fix CMakeLists.txt to include all sources

* Fix test flake in local store tests

This doesn't affect production because we always set the additional
references pointer there, but it's technically optional and some tests
don't do this.