Implement useEmulator for Firestore

[samtstern]

Discussion

This PR is part of a group: #3904 #3906 #3909

Note: I did not feel comfortable adding this to firestore-exp because I couldn't quite understand the internals and it seems like we'll need to amend the API proposal to add something like EmulatorSettings since it looks like there is no longer a global settings object. Hoping @schmidt-sebastian can do that in a follow-up PR?

Android implementation:
firebase/firebase-android-sdk#1802

This follows Proposal 2 at:
http://go/firebase-emulator-connection-api

Testing

• Added new unit tests

API Changes

• Approved, see above

[changeset-bot]

🦋 Changeset detected

Latest commit: 3332d63

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 9 packages

Name	Type
firebase	Minor
@firebase/firestore	Minor
@firebase/firestore-types	Minor
@firebase/rules-unit-testing	Patch

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[github-actions]

Changeset File Check ✅

No modified packages are missing from the changeset file.

[google-oss-bot]

Binary Size Report

Affected SDKs

• @firebase/firestore

  Type	Base (8939aec)	Head (e47a7da)	Diff
  browser	249 kB	249 kB	+335 B (+0.1%)
  esm2017	197 kB	198 kB	+317 B (+0.2%)
  main	484 kB	484 kB	+420 B (+0.1%)
  module	246 kB	247 kB	+335 B (+0.1%)
  react-native	197 kB	198 kB	+317 B (+0.2%)

• @firebase/firestore/memory

  Type	Base (8939aec)	Head (e47a7da)	Diff
  browser	186 kB	186 kB	+335 B (+0.2%)
  esm2017	147 kB	148 kB	+317 B (+0.2%)
  main	356 kB	356 kB	+420 B (+0.1%)
  module	184 kB	184 kB	+335 B (+0.2%)
  react-native	148 kB	148 kB	+317 B (+0.2%)

• firebase

  Type	Base (8939aec)	Head (e47a7da)	Diff
  firebase-firestore.js	286 kB	286 kB	+340 B (+0.1%)
  firebase-firestore.memory.js	225 kB	225 kB	+340 B (+0.2%)
  firebase.js	830 kB	831 kB	+340 B (+0.0%)

Test Logs

• Base (8939aeca): https://github.com/firebase/firebase-js-sdk/actions/runs/309602669
• Head (e47a7dad): https://github.com/firebase/firebase-js-sdk/actions/runs/310456849

[google-oss-bot]

Size Analysis Report

Affected Products

No changes between base commit (8939aec) and head commit (e47a7da).

Test Logs

• Base (8939aeca): https://github.com/firebase/firebase-js-sdk/actions/runs/309602669
• Head (e47a7dad): https://github.com/firebase/firebase-js-sdk/actions/runs/310456849

[schmidt-sebastian]

Basically LGTM. I think we should merge the two error checks that verify that the settings cannot be changed after instantiation.