fix: remove loading when stop clicked and add loading when request in…

[zixlin7]

… progress

Problem

• the initial thinking doesn't go away if you click stop button
• no thinking between iterations of requests

Solution

• in onStopChatResponse, if item type is AnswerStream update the item type to Answer
• add loading messages to the duration that we are preparing request and receive response from api

License

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.