firebase-ios-sdk

Implement unified emulator settings API proposal (#5916)

* Add header for API proposal

* Fix some bugs and add implmentation

* Fix header import

* Fix umbrella header

* Add ways to modify settings object

* Remove unnecessary nodoc

* Update with new API

* Add implementations for Firestore and RTDB

* Revert emulator settings class

* fix style

* Remove bad import and assertion on override

* Prevent database emu from being set after repo init

* Add unified emu to functions

* Add tests

* update header comment

* fix test failures

* remove unused variable

* fix database test

* cast NSInteger to long

* fix style

* Fix functions test in travis

* Remove valueForKeyPath in tests

* fix style

* update comments and remove explicit scheme

* save progress

* Implement reference validation for RTDB

* Add tests

* Add changelog entries

* Remove test logs

* Fix line lengths

* remove underlyingHost

* fix functions tests

* fix integration warnings in functions test

* fix functions test

* Fix infinite loop exposed in integration tests (#6912)

Co-authored-by: Paul Beusterien <paulbeusterien@google.com>