fix(datepicker): ISO 8601 dates decorated as invalid in forms

[Splaktar]

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PR Checklist

Please check your PR fulfills the following requirements:

• Does this PR fix a regression since 1.2.0, a security flaw, or a problem caused by a new browser version?
• The commit message follows our guidelines
• Tests for the changes have been added or this is not a bug fix / enhancement
• Docs have been added, updated, or were not required

PR Type

What kind of change does this PR introduce?

[x] Bugfix
[ ] Enhancement
[ ] Documentation content changes
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Infrastructure changes
[ ] Other... Please describe:

What is the current behavior?

• valid ISO 8601 dates are decorated as invalid in forms

Fixes #12075

What is the new behavior?

• when in updateErrorState(), we make sure that ISO 8601 strings are parsed to dates
• valid ISO 8601 dates are decorated as valid in forms

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information