Use case

The "raw" PointerEvent has a field buttons to figure what which buttons were pressed; notably in the cause of mouses it is particularly relevant to distinguish between left, right and middle clicks.

However, when using the more user-friendly recognizers, that expose events as TapUpDetails and TapDownDetails, this field is not propagated. In particularly, it is jarring to use MultiTapGestureRecognizer, because you can set a allowedButtonsFilter, but if you allow more than one type of button, you won't be able to determine which one it was (at least as far as I can tell).

Proposal

I believe adding this would be very simple, though with the caveat that if we want to avoid breaking changes we need to make it optional. I suspect that is historically how the kind field was added to TapDownDetails because is also optional (though it is required on TapUpDetails, so maybe we are willing to add a required field - honestly I don't expect users to be creating "synthetic" events all that often and would be a very simple fix if they are).

As a proof of concept, I have started working on a PR showing how it could be added (still need to add some tests, but wanted to raise the discussion on an issue first).