chore: Merged master branch into v7

[hiranya911]

I've done the bare minimal changes necessary so this branch would compile and all tests would pass. There's some room for clean up and additional tests, which I will get to in future PRs.

Notable changes/additions:

• AuthErrorHandler was moved to the internal package so the multitenancy code can use it too (via AuthHttpClient)
• Added AuthErrorCode.TENANT_ID_MISMATCH enum value.
• AuthHttpClient is now a wrapper for the ErrorHandlingHttpClient.

Conflicts were detected only in the following files:

	both modified:   src/main/java/com/google/firebase/auth/FirebaseAuth.java
	both modified:   src/main/java/com/google/firebase/auth/FirebaseTokenUtils.java
	both modified:   src/main/java/com/google/firebase/auth/FirebaseTokenVerifierImpl.java
	both modified:   src/main/java/com/google/firebase/auth/FirebaseUserManager.java
	both modified:   src/main/java/com/google/firebase/auth/internal/FirebaseTokenFactory.java
	both modified:   src/main/java/com/google/firebase/messaging/FirebaseMessagingClientImpl.java
	both modified:   src/test/java/com/google/firebase/auth/FirebaseAuthIT.java
	both modified:   src/test/java/com/google/firebase/auth/FirebaseAuthTest.java
	both modified:   src/test/java/com/google/firebase/auth/FirebaseTokenVerifierImplTest.java
	both modified:   src/test/java/com/google/firebase/auth/FirebaseUserManagerTest.java
	both modified:   src/test/java/com/google/firebase/messaging/MulticastMessageTest.java

Review effort should mostly focus on the above classes.

[hiranya911]

@micahstairs most of the files that required merging were stuff you last worked on. PTAL and call out any obvious merge errors or oversights.

[micahstairs]

Alright, I skimmed the files you listed above and didn't see any obvious merge errors!

[micahstairs]

LLC

[hiranya911]

I'll leave these instances unchanged for now since they reflect the current state of the master branch. It's best to do a separate PR in the future, and correct all these license headers in one go.

[lahirumaramba]

LGTM.
I didn't check for code that might have possibly misplaced/overwritten during the merge. Is this something we should worry about?

[hiranya911]

We have fairly good unit and integration test coverage in the affected areas. And a manual inspection didn't reveal anything unusual.