[CP] Fix dart pub login

[jonasfj]

Commit(s) to merge

42e12a50de5371b4107ae1860945dcdf6ebb32fd (sdk/+/246582)

Target

stable

Issue Description

Fix dart pub login due to unexpected null in response.

What is the fix

The command crashed because the metadata end-point returned null for
the name property. This fix handles invalid responses more gracefully,
and handles the case where name is null, by not displaying the name.

Why cherry-pick

Users who was already logged was able to continue publish packages, but
displaying the login status using dart pub login was broken.
Attempts to login would also cause a crash after successful
authentication, before credentials were saved.

Risk

low (changes only affect the dart pub login command, which is fairly broken).

Issue link(s)

dart-lang/pub#3424

Extra Info

This bumps pub_rev with two new commits, see diff: dart-lang/pub@a949b32...cherry-pick-for-2.17.2

$ git log --format="%C(auto) %h %s" a949b329b1b51f5f3973a790e0a0a45897d837de..cherry-pick-for-2.17.2 
 c66381c5 Make `name` field of `_UserInfo` nullable. Fix #3424 (#3442)
 cecc8e3c Handle broken response from userinfo_endpoint (#3427)

[jonasfj]

Update: I just realized that dart pub publish initiates a login-flow on-the-fly, and this flow does not talk to the meta-data end-point (hence, unaffected by this bug).

So users can still publish, even if they are not logged in, they just have to use dart pub publish and complete the login-flow it initiates.
But it's fair to think that some users who experience that dart pub login is broken, won't try to run dart pub publish -- since they'll think authentication is broken.

[vsmenon]

lgtm