fix(text-input): validation error appears even if field is not changed, add validateOnChange prop

[avi-alpert]

Problem

There are two issues with how validation works on TextInput

• Validation error only appears onBlur. On single-item forms this leads to a confusing UX since submit button is disabled but no error message is shown (see recording)
• Validation error message appears onBlur even when the field hasn't been changed. When a field's autofocus is true, and user clicks X to exit the form, an error message shows up. (see recording)

Solution

• Add optional validateOnChange prop to TextInput. This allows consumers to opt-in to validation happening onChange for a specific field
• Only show validation error onBlur if user has touched the field

Screen recording before fix:

Screen.Recording.2025-07-07.at.2.24.45.PM.mov

Screen recording after fix:

Screen.Recording.2025-07-07.at.2.25.31.PM.mov

Tests

• I have tested this change on VSCode
• I have tested this change on JetBrains
• I have added/updated the documentation (if applicable)

License

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.