Figure float with caption at the figure level.
```
% pandoc -f native -t jats
[Figure ("fig-id",[],[]) (Caption Nothing [Para [Str "Caption"]]) [Para [Str "Text"],
Para [Image ("fig-id-2",[],[]) [] ("foo.png", "fig:")]]]
^D
Caption
Text
```
Figure float with caption and alt text.
```
% pandoc -f native -t jats
[Figure ("fig-id",[],[]) (Caption Nothing [Para [Str "Caption"]]) [Para [Str "Text"],
Para [Image ("fig-id-2",[],[]) [Str "alt"] ("foo.png", "fig:")]]]
^D
Caption
Text
alt
```