Fix completion tuple (#14594) In progress work toward #14585 guarded eval strip leading characters until it find soemthing, this is problematic as `(1, x`, becomes valid after 1 char strip: `1, x` is a tuple; So now we trim until it is valid an not a tuple. This is still imperfect as things like `(1, a[" "].y` will be trimmed to `y`, while it should stop with `a[" "].y` ? I think maybe we should back-propagate; build back up from `y`, to `a[" "].y`, greedily until we get the last valid expression – skipping any unbalanced parentheses/quotes if we encounter imblanced.