fix: do not prevent touchend for clear button

[web-padawan]

Fixes #681

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This change is 

[tomivirkki]

This should also probably validate on a clear button tap so it would behave the same on mobile and desktop. Currently, if you have a required date-picker, it doesn't get marked as invalid if you clear the field on mobile.

[web-padawan]

Confirmed the regression (can be reproduced in Chrome mobile device emulation).

• desktop:validate() for clear button is called for empty string (correct)

• mobile: validate() for clear button is called for old value (incorrect).

So, we should call validate() in a different place.