Fix part of #5070: Display empty answer message in selection 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 "Choose an answer to continue.", is now displayed when the user attempts to submit without selecting any input.

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: ...".)
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[theMr17]

@adhiamboperes 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!

[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!

[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!

[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 only have a monor non-blocking comment on this.

[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!

[theMr17]

@adhiamboperes PTAL.

[oppiabot]

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