fix(auth, web): correct use of underlying useEmulator API, sync not async

[mikehardy]

Description

My original implementation of auth.useEmulator for FlutterFire in #4263 used the underlying firebase-js-sdk incorrectly for the web implementation

Underlying web API for useEmulator is sync not async, so attempting to await it and call .then resulted in an error since no Promise was returned.

Supporting auth.useEmulator officially should still require the Firestore issue uncovered in firebase-js-sdk >= v8.0.1 to be resolved, tracked here #4127 - but if users are willing to pin firebase-js-sdk === v8.0.1 auth.useEmulator will now work for them and firebase web in general should work

For people testing this and using firestore on web: firebase-js-sdk v8.0.1 is reported to work with auth.useEmulator without triggering the problem described in #4127 - thanks to @wtfiwtz for success report

Related Issues

Fixes #5096

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[russellwheatley]

LGTM

[wtfiwtz]

I found that this only works with the latest SDK - I was on 7.20.0 due to another issue.

<script src="https://www.gstatic.com/firebasejs/8.2.9/firebase-app.js"></script>
<script src="https://www.gstatic.com/firebasejs/8.2.9/firebase-firestore.js"></script>
<script src="https://www.gstatic.com/firebasejs/8.2.9/firebase-auth.js"></script>
<script src="https://www.gstatic.com/firebasejs/8.2.9/firebase-database.js"></script>
<script src="https://www.gstatic.com/firebasejs/8.2.9/firebase-firestore.js"></script>
<script src="https://www.gstatic.com/firebasejs/8.2.9/firebase-functions.js"></script>

... in index.html and it started working for me.

[mikehardy]

@wtfiwtz The PR comment contains that direction yes - but please read it very carefully, there is a related issue #4127 that should give you pause if you are using firestore as you indicate...

[wtfiwtz]

Thanks @mikehardy... that's why I was on 7.20.0 but it does work with 8.0.1 and doesn't trigger #4127 that way.

Cheers,
Nigel

[mikehardy]

Great - I updated the description here to be very explicit about that v8.0.1 sweet spot - thanks for the success report