feat(web): subkey menu realignment when subkey columns are even

> One small thing, the popup is typically centered over the key if space allows. When there is an odd number of columns, one choice will always be preselected if you don't move your finger. That's great and repeatable. Most of my keys have only one popup, which happens to be an odd number.
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> Unfortunately, when there are an even number of columns, it's ambiguous/fidgety which one will be selected. I don't know how many of us can regularly hit the left or right side of a key.
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> What do you think about shifting the popup display half a key left or right when there is an even number of columns so that one "default" key is unambiguously selected? If possible, I suggest it could be shifted a half-key left when the base key is on the right side of the screen (O) and a half-key right when the base key is on the left side of the screen (E).
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> Gboard does this realignment:
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_Originally posted by @MattGyverLee in https://github.com/keymanapp/keyman/issues/9698#issuecomment-1759375134_