Resolve field instance models using index when filtering errors

[kshepherd]

Description

This is a very small change that fixes form error handling for repeated fields, by correctly passing the field index to formBuilderService.findById() when resolving a parsed field to a dynamic form control model.

Without this change applied, the error is always rendered for the first element only, and in some cases does not correctly invalidate or render an error message at all.

With this change applied, the correct field instance is made invalid and the message displayed.

This might not be noticeable to many DSpace configurations since most errors are "required" errors, where by definition a repeated field is usually not empty/null, but you can test this with a custom error message, or the regex submission config validator.

Instructions for Reviewers

To test:

• Set up a repeatable onebox field (e.g. subject keyword) and give it a regex validation rule in submission-forms.xml
• Add several valid instances of the field that will match the regex. Save.
• Add an invalid instance, or change another instance to not match the regex. Save.

Without this PR applied, the error will either not display or display only for index 0.

With this PR applied, the error should display properly in the correct field index.

Checklist

• My PR is created against the main branch of code (unless it is a backport or is fixing an issue specific to an older branch).
• My PR is small in size (e.g. less than 1,000 lines of code, not including comments & specs/tests), or I have provided reasons as to why that's not possible.
• My PR passes ESLint validation using npm run lint
• My PR passes all specs/tests and includes new/updated specs or tests based on the Code Testing Guide.
• My PR includes details on how to test it. I've provided clear instructions to reviewers on how to successfully test this fix or feature.

[pcg-kk]

Look fine for me - error not happen anymore

[tdonohue]

@kshepherd : from looking at form.component.ts on dspace-7_x, it looks like this might impact that release as well. The code at least looks the same. Do you agree?

[kshepherd]

@tdonohue agreed! i added the label, thanks

[tdonohue]

👍 Code makes sense to me. Thanks @kshepherd !

[dspace-bot]

Successfully created backport PR for dspace-7_x:

• [Port dspace-7_x] Resolve field instance models using index when filtering errors #4450

[dspace-bot]

Successfully created backport PR for dspace-8_x:

• [Port dspace-8_x] Resolve field instance models using index when filtering errors #4451

[dspace-bot]

Successfully created backport PR for dspace-9_x:

• [Port dspace-9_x] Resolve field instance models using index when filtering errors #4452