Fix event target

[roderickhsiao]

1. In click handler we directly check if the target node is button/anchor, this should be currentTarget instead of target or else some case like keyboard enter for a button component will not identify as button as the target will be the child.
2. We only check if a button tag has form and submit it by default without checking the type of the button. If a button (with type button specified), javascript will still attach form object to the element, but browser won't auto submit it when clicking it. To align with the browser behavior, I'm adding check to prevent auto-submit parent form if the button type is not submit (default)

All child component for auto scan case should already attached different listeners. (we are not using capture in the click handler)

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