Wire: Feature suggestion: Dedicated per-Wire version chooser input for blend modes

[webel]

A frequently useful input control is the ability to choose a blend mode for a VideoMixer. This can be achieved using a Choice In and a lot of patience assigning options to integers that match blend modes, but this is then specific to a particular version of Wire (to the blend modes available for that version). If the Wire version changes this can break.

It would be handy to have a dedicated Blend Mode Chooser input control that has the correct named blend mode Integer choices for each particular version of Wire, and is guaranteed to work correctly on version upgrades.