Added DiffUtil

[hanupratap]

Hey, I have added DiffUtil in QuestionnaireListAdapter to improve performance at later stages.

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[hanupratap]

Thanks for your pull request. It looks like this may be your first contribution to a Google open source project (if not, look below for help). Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

📝 Please visit https://cla.developers.google.com/ to sign.

Once you've signed (or fixed any issues), please reply here with @googlebot I signed it! and we'll verify it.

What to do if you already signed the CLA

Individual signers

• It's possible we don't have your GitHub username or you're using a different email address on your commit. Check your existing CLA data and verify that your email is set on your git commits.

Corporate signers

• Your company has a Point of Contact who decides which employees are authorized to participate. Ask your POC to be added to the group of authorized contributors. If you don't know who your Point of Contact is, direct the Google project maintainer to go/cla#troubleshoot (Public version).
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[jingtang10]

Thanks for the PR!

What made you decide to use the AsyncListDiffer rather than ListAdapter?

[jingtang10]

these two lines seem wrong?

[jingtang10]

i don't belive this is correct. it's possible the same path can be used in two differnt items (not the least because of #244).

[jingtang10]

why inner?

[jingtang10]

Is this still being worked on? If not please close this PR.

[jingtang10]

please feel free to reopen.