I've been having wrong understanding of spec since implementing WebDriver touch support

• webdriver: Add touch support for all platforms #41067
• webdriver: Enable testdriver tests for Touch by always dispatching embedder MouseMove #41171.

We should not try-hard to fire an embedder event in this case according to spec.

This would unblock:

• servodriver always sets a pointerId of 0 for move events #41250
• script: Implement pointer events #41290
• webdriver: Enable testdriver tests for Touch by always dispatching embedder MouseMove #41171 (review)