bug(form-field): userAriaDescribedBy type error

[wagnermaciel]

Issue Summary

For some reason userAriaDescribedBy was showing up as an object in one of our internal tests. This meant that the call to userAriaDescribedBy.split threw errors and caused that test to fail.

Temporary Fix

Our temporary fix is to check the type of userAriaDescribedBy to ensure calling .split does not throw any errors.

#20401

Desired Solution

Figure out where the gap in type checking is and close it so that we don't need to check the type of userAriaDescribedBy here.