FIO-3703: Fixes an issue where NestedData components with modal view do not render values inside Layout components in modal preview table

[alexandraRamanenka]

Link to Jira Ticket

https://formio.atlassian.net/browse/FIO-3703

Description

NestedDataComponent was not iterating through layout components to render the values of the components inside them. Also, getComponents method was checking only in rowIndex is undefined, but it also could be null because inside everyComponent method it is set to null if not provided.

Dependencies

This PR depends on the following PRs from other Form.io modules: ...

How has this PR been tested?

I added automated tests to cover [all/the following] cases, including ...

Checklist:

• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (if applicable)
• My changes generate no new warnings
• My changes include tests that prove my fix is effective (or that my feature works as intended)
• New and existing unit/integration tests pass locally with my changes
• Any dependent changes have corresponding PRs that are listed above