firebase-ios-sdk

add heartbeat feature for ios sdks (#4098)

* add heartbeat feature

* fix client logtype

* make class functions

* add subspec changes

* remove test file

* add heartbeat  tests

* use FileDataStorage instead of Storage

* add style

* use file data storage instead of storage

* fix test location

* add tests

* address comments

* update storage heartbeat with the new api

* update format

* update formatting and use correct enums

* rename

* update storage

* fix heartbeat

* update heartbeat tests

* fix styling

* Revert change

* heartbeat storage

* add comments

* update storage

* address comments

* add comments

* address comments

* fix style

* add style

* add style

* move heartbeat date storage

* move to environment

* update tests

* add tests

* small change

* add google utilities

* delete the header file

* update tests

* remove headers

* fix comment

* gul heartbeat date storage

* Update versions for heartbeat PR (#4311)

* update podfile

* Fix Firestore build under CMake

GoogleUtilities must now build SecureCoding