Update citations samples with title and nullable uri

[andrewheard]

Updated the citations samples to include cases where the response has a title instead of a uri. This scenario was reported in firebase/firebase-ios-sdk#13518.

[github-actions]

Coverage Diff

GenerateContentResponse: 40
| candidates: 37
| | citationMetadata: 4
| | | citations: 4
| | | | title: 0 -> 2 ✅
Total Coverage: 42.74% -> 43.55% ✅

Legend:
✅ : total coverage increase
🔵 : files number increase, total coverage unaffected
🟡 : files number decrease, total coverage unaffected
❌ : total coverage decrease

[rlazo]

I'll track fixing the Android test to correctly handle these cases. You can go ahead and merge the change.

[andrewheard]

cc: @hsubox76 I think the JS SDK already handles uri and title correctly. I think changing https://github.com/firebase/firebase-js-sdk/blob/f7c6dc4fe10ca3999b1499476ecf9b911c534d25/packages/vertexai/src/requests/stream-reader.test.ts#L213 from 2 to 3 will resolve the test failure when we tag the next major version.

[dlarocque]

JS Unit tests should be passing after firebase/firebase-js-sdk#8445