all: rename io/event.Key to Tag

Key had an unfortunate association with keyboard input.

This is an API change. The following rewrites were run to fixup
Gio code:

        $ gofmt -r 'pointer.InputOp{Key:a} -> pointer.InputOp{Tag:a}' -w .
        $ gofmt -r 'pointer.InputOp{Key:a, Grab:b} -> pointer.InputOp{Tag:a, Grab:b}' -w .
        $ gofmt -r 'key.InputOp{Key:a} -> key.InputOp{Tag:a}' -w .
        $ gofmt -r 'key.InputOp{Key:a, Focus:b} -> key.InputOp{Tag:a, Focus:b}' -w .
        $ gofmt -r 'event.Key -> event.Tag' -w .

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

io/pointer/pointer.go

@@ -57,7 +57,7 @@ type AreaOp struct {
 // InputOp declares an input handler ready for pointer
 // events.
 type InputOp struct {
-	Key event.Key
+	Tag event.Tag
 	// Grab, if set, request that the handler get
 	// Grabbed priority.
 	Grab bool
@@ -155,7 +155,7 @@ func (op AreaOp) Add(o *op.Ops) {
 }
 
 func (h InputOp) Add(o *op.Ops) {
-	data := o.Write(opconst.TypePointerInputLen, h.Key)
+	data := o.Write(opconst.TypePointerInputLen, h.Tag)
 	data[0] = byte(opconst.TypePointerInput)
 	if h.Grab {
 		data[1] = 1