refactor: migrate attachment validator to ts

[tshuli]

Problem

Part of #7

Solution

Improvements

• Migrates attachment validation to Typescript

Unit test coverage

Attachment validation
    check for responses on hidden fields should disallow responses submitted for hidden fields
      ✓ when response contains filename
      ✓ when response contains answer
      ✓ when response contains file content

    Validation of attachment size
      ✓ should respect the attachmentSize from formField
      ✓ should allow attachment with valid size
      ✓ should disallow attachment that exceeds size

    Required or optional
      ✓ should disallow submission with no attachment if it is required 
      ✓ should allow submission with attachment if it is required 
      ✓ should allow submission with attachment if it is optional 
      ✓ should allow submission with no attachment if it is not required
      ✓ should disallow submission with no answer if it is required 
      ✓ should allow submission with no answer if it is not required 
      ✓ should disallow when it is not required but with answer and no attachment

Tests

• Create two required attachment fields with 1mb size limit each. Hide one of them behind logic. Check that normal submission using frontend succeeds for both visible and hidden field.
• Check that following validation works when submitting programatically
• Attachment size cannot be above the specified limit. Use the AngularJS inspector to modify field size limit to 2mb on frontend. Upload a file of >1mb. Check that submission is rejected "File size more than limit"
• Attachment cannot be empty if required. First submit a form with the second attachment field hidden. Programatically resubmit with the second field unhidden but with no answer or attachment. Check that submission is rejected "Answer is empty string"
• Now inject an answer into the response for the unhidden field but with no attachment content. Check that submission is rejected "No attachment content"

[liangyuanruo]

was AttachmentValidator.js deleted?

[mantariksh]

some refactors requested on the tests!

[tshuli]

@mantariksh thanks for reviewing, comments addressed for re-review

[tshuli]

Addressed comments, for re-review @mantariksh