fix: parsing text input problems

[navinkarkera]

Description

Fix for #1460

Discovered other issues while working on above issue.

• Error while saving a text problem without entering second answer text box.
• In text input problem, if we enter feedback to second or third answer (incorrect) field, the feedback is moved to previous answer, i.e. feedbacks shift up by 1.
  • To test this issue, checkout the first commit in this PR.

Supporting information

• Part of Text input is opened in HTML if an additional answer is added #1460
• Private-ref: FAL-4087

Testing instructions

• Follow instructions in Text input is opened in HTML if an additional answer is added #1460 and verify that editors do not default to advanced editor.
• And verify the above listed issues are also fixed

Other information

Found one more issue but did not fix it as part of this PR:

If incorrect answers are entered before correct answer in text input problems, they are lost.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.34%. Comparing base (7e4ecff) to head (ae97545).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1679      +/-   ##
==========================================
+ Coverage   93.33%   93.34%   +0.01%     
==========================================
  Files        1108     1108              
  Lines       22045    22050       +5     
  Branches     4674     4757      +83     
==========================================
+ Hits        20575    20583       +8     
+ Misses       1405     1396       -9     
- Partials       65       71       +6     

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