fix: InputGroup validation changes

[jacobdevera]

Description

BREAKING CHANGE
Refactor _FormValidationOverlay in InputGroup and related components

• InputGroup will now always render with a _FormValidationOverlay regardless of whether a validation state is present or not. This prevents the component from throwing away the old input element and losing the previous state when the validation state changes.
  • fixes an issue with ComboboxInput that makes it impossible to enter input
  • fixes an issue with DatePicker that would cause it to lose focus when closing the Calendar with the Esc key
• only show _FormValidationOverlay if text is present in validationState with a valid string
• remove validationOverlayProps from SearchInput as this would now be handled by passing them into inputGroupProps
• add formMessageProps to SearchInput to handle passing props into its own FormMessage

fixes #1207

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[meganaconley]

Tested locally, inputs no longer lose focus after validation.