firebase-ios-sdk

Add support for running Firestore integration tests (#2660)

* Add Firestore_IntegrationTests_macOS to Xcode

* Change deployment target from 10.14 to 10.10

* Make standard target edits

  * Force C99/C++11
  * Use shared test info.plist
  * Remove CODE_SIGN_IDENTITY

* Add Firestore_IntegrationTests_macOS to the Podfile

* Have sync_project handle macOS integration tests

* Pod install and sync_project

* Add header search paths and ldflags

* Build integration tests on macos

* Remove integration tests from unit tests

* Make Firestore_IntegrationTests_macOS buildable from the command-line