animator_uid matches a uid before an index, so an animator whose uid
equals an index is picked over the one at that position. The four
commands that take `animator` (layer.addTextAnimatorProperty,
layer.addTextSelector, text.addSelector, text.animatorFontAxes) now say
so; text.addSelector also said only `uid|index` before. The test gives a
second animator uid 1 and checks that `animator: 1` picks it.
layer.addTextAnimatorProperty, layer.addTextSelector and
text.animatorFontAxes take `animator: uid|index`, counted from 1 as the
code and `#n` references do, but the parameters didn't say so and
`animator: 0` failed with only "no animator 0". The parameters now say
1-based, and the error says what the value can be.