gpu: build gpu data also when outside window

This commit fixes a bug where a shape first drawn off-screen
and later moved into screen would not display properly. Since we
cache CPU operations (vertex transform / construction) we need to
upload the constructed data to the GPU after it was build, or a later
frame will use non-initialized memory for it's draw call.

Note that this fix removes the optimization of not processing clip
paths outside the screen - but this is assumed to be uncommon except
when it is first drawn off screen to later be moved in (e.g. in a scrolling list)
in which case we do want to upload the data and prepare for that later
call.

This commit also does a few minor clean ups and adds a test case.

Signed-off-by: Viktor <viktor.ogeman@gmail.com>

internal/ops/reader.go

@@ -62,11 +62,11 @@ func (r *Reader) Reset(ops *op.Ops) {
 }
 
 func (k Key) SetTransform(t f32.Affine2D) Key {
-	sx, hx, sy, hy, _, _ := t.Elems()
+	sx, hx, _, hy, sy, _ := t.Elems()
 	k.sx = sx
 	k.hx = hx
-	k.sy = sy
 	k.hy = hy
+	k.sy = sy
 	return k
 }