FIO-8389: Fix EditGrid with Empty/Is Not Empty conditional logic in there

Link to Jira Ticket

What changed?

Previously, @formio/core would fail to call 'isEmpty' method if it doesn't exist. This PR adds a check to make sure it exists, before calling.

Test is added in formio.js

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[x] My changes generate no new warnings
[x] My changes include tests that prove my fix is effective (or that my feature works as intended)
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