io/pointer: [API] rename PointerEvent.Type to Kind

Kind is the idiomatic field name for distinguishing a struct without
using separate types.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

widget/widget_test.go

@@ -35,12 +35,12 @@ func TestBool(t *testing.T) {
 	r.Queue(
 		pointer.Event{
 			Source:   pointer.Touch,
-			Type:     pointer.Press,
+			Kind:     pointer.Press,
 			Position: f32.Pt(50, 50),
 		},
 		pointer.Event{
 			Source:   pointer.Touch,
-			Type:     pointer.Release,
+			Kind:     pointer.Release,
 			Position: f32.Pt(50, 50),
 		},
 	)