FIO-10165: Fix issue about the informative error messages are missing…

[yauheni-formio]

… in FMG and FVP

Link to Jira Ticket

https://formio.atlassian.net/browse/FIO-10165

Description

This bug happened after changing Core library in Formio.ts file (commit 0f1a86a7fd2ddd49161262bc899b9af01c2d1788) 3 months ago. Instead of an error string server started returning an object error.

Breaking Changes / Backwards Compatibility

n/a

Dependencies

n/a

How has this PR been tested?

manually

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