Fix part of #5070: Display empty answer message in drag & drop sort interaction

[theMr17]

Explanation

Fixes part of #5070

Enables the submit_answer_button when the pending answer is empty. Instead of disabling the button, an error message, stating "Arrange the boxes to continue.", is now displayed when the user attempts to submit without arranging the boxes.

Screen.Recording.mp4

Essential Checklist

• The PR title and explanation each start with "Fix #bugnum: " (If this PR fixes part of an issue, prefix the title with "Fix part of #bugnum: ...".)
• Any changes to scripts/assets files have their rationale included in the PR explanation.
• The PR follows the style guide.
• The PR does not contain any unnecessary code changes from Android Studio (reference).
• The PR is made from a branch that's not called "develop" and is up-to-date with "develop".
• The PR is assigned to the appropriate reviewers (reference).

For UI-specific PRs only

If your PR includes UI-related changes, then:

• Add screenshots for portrait/landscape for both a tablet & phone of the before & after UI changes
• For the screenshots above, include both English and pseudo-localized (RTL) screenshots (see RTL guide)
• Add a video showing the full UX flow with a screen reader enabled (see accessibility guide)
• For PRs introducing new UI elements or color changes, both light and dark mode screenshots must be included
• Add a screenshot demonstrating that you ran affected Espresso tests locally & that they're passing

[oppiabot]

Hi @theMr17, I'm going to mark this PR as stale because it hasn't had any updates for 7 days. If no further activity occurs within 7 days, it will be automatically closed so that others can take up the issue.
If you are still working on this PR, please make a follow-up commit within 3 days (and submit it for review, if applicable). Please also let us know if you are stuck so we can help you!

[theMr17]

@adhiamboperes PTAL.

[oppiabot]

Unassigning @theMr17 since a re-review was requested. @theMr17, please make sure you have addressed all review comments. Thanks!

[oppiabot]

Hi @theMr17, I'm going to mark this PR as stale because it hasn't had any updates for 7 days. If no further activity occurs within 7 days, it will be automatically closed so that others can take up the issue.
If you are still working on this PR, please make a follow-up commit within 3 days (and submit it for review, if applicable). Please also let us know if you are stuck so we can help you!

[adhiamboperes]

Thanks @theMr17!

PTAL.

[oppiabot]

Hi @theMr17, I'm going to mark this PR as stale because it hasn't had any updates for 7 days. If no further activity occurs within 7 days, it will be automatically closed so that others can take up the issue.
If you are still working on this PR, please make a follow-up commit within 3 days (and submit it for review, if applicable). Please also let us know if you are stuck so we can help you!

[adhiamboperes]

Thanks @theMr17. I tested this code manually and noticed a bug. PTAL.

[oppiabot]

Unassigning @adhiamboperes since the review is done.

[oppiabot]

Hi @theMr17, it looks like some changes were requested on this pull request by @adhiamboperes. PTAL. Thanks!

[adhiamboperes]

Please also add tests to verify that the submit button is re-enabled and the error message is hidden once a drag/sort interaction occurs.

[theMr17]

@adhiamboperes PTAL. I have made the requested changes and have also added tests to verify that the submit button is re-enabled and the error message is hidden once a drag/sort interaction occurs for both grouping and non-grouping drag & drop interactions.

[oppiabot]

Unassigning @theMr17 since a re-review was requested. @theMr17, please make sure you have addressed all review comments. Thanks!

[adhiamboperes]

Thanks @theMr17! This LGTM.

[oppiabot]

Unassigning @adhiamboperes since they have already approved the PR.

[oppiabot]

Hi @theMr17, this PR is ready to be merged. Please address any remaining comments prior to merging, and feel free to ask someone to merge your PR once the CI checks pass and you're happy with it. Thanks!