Element click behavior on touchscreen devices

This is a follow-up from the Chrome Driver issue https://issues.chromium.org/issues/42320346.

The element click spec currently assumes a mouse interaction. However, it is desirable for element click to produce touch events (touchstart, touchend) when webdriver tests are run on touchscreen mobile devices, as a real user would use a tap gesture there, and many mobile sites are listening only for touch events.

Some corner cases need to be considered here:

• A desktop device with a touchscreen could mean there is a mouse as well as a touchscreen, in which case generating touch events by default may not be desirable.
• When emulating a mobile touchscreen device on desktop, it may need to behave similar to a real touchscreen-only device and generate touch events there as well.

It would be good to get clarification on whether touch events should be generated when performing an element click and how to ensure it is done where only touch and no mouse interactions are expected.

Alternatively, should there be a separate element tap command instead?

Start with the linked WebDriver element click specification and the referenced Chrome Driver issue. Review the touchscreen-only, desktop-touchscreen, and emulated-mobile cases described here, then determine whether element click should generate touch events or whether a separate tap command is needed. Done means the behavior and applicable cases are clarified in the specification.