FIO-8968: Displaying counter when toggle preview button

[yauheni-formio]

Link to Jira Ticket

https://formio.atlassian.net/browse/FIO-8968

Description

Fixed display of word and character counter when we hide and show preview of component. The default value index = 0 was added because in the case of the first render or click on the show/hide preview button we did not have access to index and index was undefined. It was the reason why the logic for setting the counter values didn't work.

Breaking Changes / Backwards Compatibility

n/a

Dependencies

n/a

How has this PR been tested?

I added unit test.

Checklist:

• I have completed the above PR template
• 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