Error handling revamp for the custom token creation API - #366

* Added core types for the error handling revamp (#350)

* Added core types for the error handling revamp

* Fixed copyright year

* Added ErrorHandlingHttpClient API (#353)

* Added core error handling abstractions

* Added unit tests for the new functionality

* Exposed getErrorCode as getErrorCodeNew

* Enabled error code assertions

* Error handling revamp for the FirebaseMessaging API (#357)

* Added core error handling abstractions

* Added unit tests for the new functionality

* Exposed getErrorCode as getErrorCodeNew

* Enabled error code assertions

* Error handling revamp for FCM APIs

* Cleaned up the FirebaseMessagingException

* Cleaned up the AbstractHttpErrorHandler class

* Updated tests

* Error handling revamp for FirebaseInstanceId API (#359)

* Delete instance ID API error handling revamp

* Added tests for IO and parse errors

* fix(auth): Migrated user management APIs to the new error handling scheme (#360)

* Error handling revamp in FirebaseUserManager

* Updated integration tests; Added documentation

* Assigning the correct ErrorCode for auth errors

* Moved AuthErrorHandler to a separate top-level class

* Error handling revamp for token verification APIs (#362)

* Error handling revamp for token verification APIs

* Updated javadocs

* Error handling revamp for the custom token creation API (#366)

* Error handlign revamp for the custom token creation API

* Using the correct authorized HTTP client for IAM requests

* Error handling revamp for the project management API (#367)

* Error handling revamp for the project management API

* Minor code and test cleanup

* Fixed some lint errors; Removed requestFactory reference from project mgt service impl

* Renamed getErrorCodeNew() to getErrorCode() (#379)

* Minor code and test cleanup

* Renamed getErrorCodeNew() to getErrorCode() in FirebaseException

* Fixing checkstyle error

* Fixing some deprecation warnings (#380)

* Handling IID error codes correctly (#381)

* Removed old deprecated APIs (#383)

* fix: Removed unused FirebaseAppStore abstraction (#427)

* fix: Removed unused FirebaseAppStore abstraction

* Using the keySet of App instances to populate the app names list

* chore: Removing redundant test dependency (#441)

* chore: Make user import hashing classes final (#425)

* chore: Merged with v7 branch with master (#456)

* fix(fcm): Replacing deprecated Batch API constructor (#460)

* fix: Handling http method override in ErrorHandlingHttpClient (#459)

* fix: Handling JSON serialization/response interception at ErrorHandlingHttpClient (#462)

* fix: Handling JSON serialization and response interception at ErrorHandlingHttpClient

* fix: Removing redundant method override header

* feat: Added new error codes for IdP management and multitenancy (#458)

* feat: Added new error codes for IdP management and multitenancy

* fix: Updated integration tests

* fix: Renamed helper method

* fix: Removing some calls to deprecated APIs (#464)

* chore: Support for specifying query parameters in HttpRequestInfo (#463)

* chore: Support for specifying query parameters in HttpRequestInfo

* fix: Removing redundant JsonObjectParser from HttpClient

* fix: Fixing a series of javadoc warnings (#466)

* fix: Made some APIs on AbstractFirebaseAuth.Builder package-protected for consistency

* Apply suggestions from code review

Co-authored-by: egilmorez <egilmore@google.com>
Co-authored-by: Kevin Cheung <kevinthecheung@users.noreply.github.com>

* fix: Minor updates to API ref docs based on code review comments

* fix: Fixing API doc wording

Co-authored-by: Horatiu Lazu <horatiulazu@gmail.com>
Co-authored-by: egilmorez <egilmore@google.com>
Co-authored-by: Kevin Cheung <kevinthecheung@users.noreply.github.com>