Enable getting a user by their federated IdP UID

[jeromegamez]

This is based on and replaces #1000 with the following changes/additions:

• Changed tests so they run within the emulator test suite and not in the integration test suite
  • This allows for a happy path and an unhappy path test
  • Instead of using a dummy IdP, the real™/emulated phone IdP can be used
• Updated documentation and changelog

Thank you @mkilmanas for the great work and collaboration in #1000, the commit of this PR is attributed to us both!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.49%. Comparing base (00f2564) to head (bdc2bb9).
Report is 4 commits behind head on 7.x.

❗ There is a different number of reports uploaded between BASE (00f2564) and HEAD (bdc2bb9). Click for more details.

HEAD has 1 upload less than BASE

Flag	BASE (00f2564)	HEAD (bdc2bb9)
integration	1	0

Additional details and impacted files

@@              Coverage Diff              @@
##                7.x    #1003       +/-   ##
=============================================
- Coverage     90.02%   71.49%   -18.54%     
- Complexity     1443     1446        +3     
=============================================
  Files           140      140               
  Lines          4192     4203       +11     
=============================================
- Hits           3774     3005      -769     
- Misses          418     1198      +780     

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[mkilmanas]

Hey @jeromegamez - thanks for pushing this though the finish line. However, I see that this PR was merged 1 day after the latest release was tagged. Are there any plans when the next release might get tagged? Still waiting for this functionality to become publicly available 😄

[jeromegamez]

Shoot, I thought I did! I will create a new release later today!

[jeromegamez]

Have I mentioned that my days have 48h and that's why you think I'm late but I'm actually not! 😅

Anyway, at last, the release is here: https://github.com/kreait/firebase-php/releases/tag/7.20.0

Thanks again!