Support for `input.PointerCancelAction`

[Lightning00Blade]

No reference or discussion about this was found on the PR that introduced the Input module - #175
The classic spec supports this command - https://www.w3.org/TR/webdriver2/#pointer-input-source
Was this an oversight or there is a reason for not support this?
CC @jgraham as writer of the PR.

[whimboo]

It looks like that we missed to add this specific action. We even don't have WebDriver classic tests so we didn't notice when porting all the existing tests for BiDi.

[whimboo]

Actually see w3c/webdriver#1216 as well. So not even sure we actually want / need that?

@jgraham what should we do with this action? Shall we remove it?