Stop using AppEngine to check database mode

[joehan]

Description

Recently, we stopped automatically creating & linking AppEngine apps to Firestore on creation (https://cloud.google.com/firestore/docs/app-engine-requirement). However, firebase init was still checking for the location of this app, and relying on it to check what mode the database was in. We now instead check via the firestore API (https://cloud.google.com/firestore/docs/reference/rest/v1/projects.databases#DatabaseType) and skip the default resource location check.

Fixes #5230 and #5452

Scenarios Tested

Created a new project, and created a Firestore DB. Checked that Cloud Resource location was not set yet (via the Firebase console settings page), and then confirmed that firebase init firestore then firebase deploy run without errors.

[codecov-commenter]

Codecov Report

Base: 56.39% // Head: 56.40% // Increases project coverage by +0.00% 🎉

Coverage data is based on head (92f8291) compared to base (225c1d7).
Patch coverage: 50.00% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5261   +/-   ##
=======================================
  Coverage   56.39%   56.40%           
=======================================
  Files         313      313           
  Lines       21245    21243    -2     
  Branches     4336     4336           
=======================================
  Hits        11982    11982           
+ Misses       8223     8221    -2     
  Partials     1040     1040           

Impacted Files	Coverage Δ
src/firestore/checkDatabaseType.ts	40.00% <40.00%> (ø)
src/init/features/firestore/index.ts	88.00% <100.00%> (-0.89%)	⬇️
src/emulator/auth/state.ts	85.43% <0.00%> (+0.56%)	⬆️

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