Fixes https://gitlab.com/kicad/code/kicad/issues/14276
Moves forced-transparency setting down into VIEW_ITEM so that it can be used to place forced-transparent objects in a different target. This keeps EnableDepthTest() from equalizing the alpha values between the two symbols (or two footprints).
Fixes https://gitlab.com/kicad/code/kicad/issues/13736