`#alternatives` are hidden when used alongside `#pause` or `#one-by-one`

[luewolf]

Using alternatives alongside pause/one-by-one will skip the first few alternatives if #alternatives is not the first element that is being displayed.

Examples:

#slide[
  foo #pause #alternatives[bar][baz] # pause foobar
]
// or
#slide[
  #one-by-one([foo], alternatives[ bar][ baz], [ foobar])
]

• Expected result: Slides [foo][foo bar][foo baz][foo baz foobar]
• Actual result: Slides [foo][foo baz][foo baz foobar]

Sure, it's possible to pass a start index to #alternatives, but that can lead to bugs when adding/removing pauses to a slide and forgetting to update the indices of alternatives on that slide.