Implement form response validation

[otomn]

Implement form response validation that takes a SDCForm and a SDCFormResponse and verify that the form response is valid against the given form.

Prerequisite:

• All provided objects are valid
• When submitted, for each SDCQuestion, there must be a corresponding SDCAnswer unless the question is disabled
• If there is no response to the question, the submitter still needs to submit an SDCAnswer, but the responses attribute can be an empty list
• For TextField, the frontend should use textFieldTypeMeta.processor to format the field before calling the validator

Requirements:

• If any prerequisite is not meet, the validator should throw an error
• Otherwise, the validator should return a list of errors identified in the answers
• Validation logic:
  • TextField:
    • Try to parse the field using the corresponding textFieldTypeMeta.parser
    • On error, add the error to the list of errors
  • ListField:
    • Verify all items in the responses are IDs of ListItems of the current list, if not, throw a validation error
    • Verify the number of selections is within maxSelections and minSelections
    • Verify if selectionDeselectsSiblings is true, there is only one selection
    • When selectionDisablesChildren is true, set flag to bypass children validation of that item
    • When an item is not selected, set flag to bypass textResponse validation of that item
• The validator should check the SDCNodes recursively
• When all checks are complete, delete all answers that are not validated

General guideline for error type:

• If the issue is likely caused by a bug in the code, throw ValidationError
• If the issue is likely caused by the user, return AnswerValidationError

[otomn]

Current progress at 670b5b5

• Finalized FormResponseValidator API
• Added basic framework, including recursion logic
• Committing code and handing over to

  Remaining work

• Add actual validation for text and list fields
• Add appropriate by pass flags
• Add each validated question to validatedAnswers
• Everything else should work fine as is, hopefully

[otomn]

@Timmarus Handing over to you