[android][database] database improvements

[Salakar]

Summary

Includes the following fixes and associated tests:

• Database listeners now correctly tearing down between RN reloads, additionally the correct react context is now used rather than old references to former instances (fixes handler on a dead thread event issue)
  • Fixes Firebase.database().ref().on() fires only once with Live Reload #1498 firebase.database().ref('Users/').on('value', function (snapshot) {console.log(snapshot.val());}); unable to get data #1611 firebase.database().ref("path").once("value") don't call callback #1609
• Fixed an issue where Reference.toString() incorrectly contains // instead of / when joining the parent and child paths
• Rework .push() behaviour to match WebSDK and correctly return a Reference instance in all scenarios
  • Fixes [WEB SDK COMPAT] await .push() returns null, but works on web sdk #893 Returning Reference instance from async await method causes an exception. #1464 After pushing data to firebase database I get null instead of snapshot in then() #1572

Checklist

• Supports Android
• Supports iOS
• e2e tests added or updated in /tests/e2e/*
• Updated the documentation in the docs repo
• Flow types updated
• Typescript types updated

Test Plan

N/A

Release Plan

• [ANDROID] [BUGFIX] [DATABASE] - Database listeners now correctly tearing down between RN reloads. (Fixes Firebase.database().ref().on() fires only once with Live Reload #1498 firebase.database().ref('Users/').on('value', function (snapshot) {console.log(snapshot.val());}); unable to get data #1611 firebase.database().ref("path").once("value") don't call callback #1609)
• [JS] [BUGFIX] [DATABASE] - Fixed an issue where Reference.toString() incorrectly contains // instead of / when joining the parent and child paths.
• [JS] [BUGFIX] [DATABASE] - Rework .push() behaviour to match WebSDK and correctly return a Reference instance in all scenarios. (Fixes [WEB SDK COMPAT] await .push() returns null, but works on web sdk #893 Returning Reference instance from async await method causes an exception. #1464 After pushing data to firebase database I get null instead of snapshot in then() #1572)
• [JS] [ENHANCEMENT] [UTILS] - Added a firebase.utils().database.cleanup() utility method which removes all database listeners.

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[codecov]

Codecov Report

Merging #1619 into master will increase coverage by 4.55%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1619      +/-   ##
==========================================
+ Coverage   71.08%   75.64%   +4.55%     
==========================================
  Files          71       72       +1     
  Lines        1840     1827      -13     
==========================================
+ Hits         1308     1382      +74     
+ Misses        532      445      -87

[Salakar]

I still need to update/add more tests for database before I merge this, but if anyone with the tagged issue could test it that'd be super helpful👌

[jch28]

nice