These arrays were declared using the pre-C99 gcc extension which treated
any trailing array in a struct as potentially flexible in length.
Change them to be C99 flexible arrays, annotate them with
`G_COUNTED_BY`, and adjust the size calculations of the overall structs
to match. The size of the overall struct will have decreased as `sizeof
(struct->my_flexible_array)` is `sizeof (*struct->my_flexible_array)` if
`my_flexible_array[1]` is used in the definition, whereas it’s zero if
C99 `my_flexible_array[]` syntax is used.
See https://people.kernel.org/kees/bounded-flexible-arrays-in-c#replace-1-element-arrays
I found the declarations using:
```sh
git grep '\[1\];' | grep -v '='
```
Signed-off-by: Philip Withnall <pwithnall@gnome.org>
1f9bcba295