feat!: forward port to firebase-ios-sdk v7+ / firebase-android-sdk v26+

[mikehardy]

Description

This is a forward port of FlutterFire to firebase-ios-sdk v7+ and firebase-android-sdk v26+

Each commit may be viewed in isolation, and in fact that is recommended.

Related Issues

Unsure if there are other issues to relate but:
#4013 - updating to SDK26 for firestore
#3969 - auth useEmulator discussion - it is gated on this but is trivial once the forward port is done

Checklist

This is my first Dart code, first Flutter code, and first batch of FlutterFire PRs
I did the same port for react-native-firebase though, so I'm new here but have been in the area a lot. Be gentle ;-)

I am not sure what should be done in the CHANGELOG or with regard to version numbers here.

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• My PR includes unit or integration tests for all changed/updated/fixed behaviors (See Contributor Guide).
• All existing and new tests are passing.
• I updated/added relevant documentation (doc comments with ///).
• The analyzer (flutter analyze) does not report any problems on my PR.
• I read and followed the Flutter Style Guide.
• I signed the CLA.
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

iOS minimum deployment target is moved to 10+
RemoteConfig debugMode no longer exists. minimumFetchTime / fetchTimeout replace it

• Yes, this is a breaking change (please indicate a breaking change in CHANGELOG.md and increment major revision).
• No, this is not a breaking change.

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[mikehardy]

@Salakar / @Ehesp this is ready for review, I believe iOS and Android are both working now, should clear the way for auth emulator as a quick followon

I understand there may be concurrent work with regards remote-config port, happy to coordinate on that though I was very very light with regards to my forward-port treatment of it here and kept the commits pretty granular so it should be easy to deal de-conflict / integrate

[mikehardy]

GitHub actions aren't wrapped in retry so the android gradle ones flake without recovering as they attempt to pull remote dependencies. Something like this would fix it though it will need to be flutter-ified invertase/react-native-firebase@f1b9af9

Here's a first cut at de-flaking E2E: #4265

One of the storage tests flaked for ios, it's passed before during this PR development and passes locally so should be unrelated to the commit:

[firebase_storage_example]:   updateMetadata
[firebase_storage_example]:      ✔ updates metadata
[firebase_storage_example]:      ✘ errors if metadata update removes existing data
[firebase_storage_example]:        [E]: Expected: {'action': 'updateMetadata test'}
[firebase_storage_example]:               Actual: {'activity': 'test', 'action': 'updateMetadata test'}

If you retry both (I don't have permission) it should go green after one or two attempts, they work locally each time

[russellwheatley]

Ahoy @mikehardy, looking good, just a couple of minor points that I think might be an issue.

[russellwheatley]

LGTM

[Salakar]

LGTM