Add support for multiple figcaption elements

This should work along with the multiple images in one ``:


Will also need to continue to number figures accordingly, so will probably either need to count the ``s rather than the images?

Start by reviewing the existing figure and caption behavior, then reproduce the issue's example with multiple images and multiple elements. The change is done when captions are supported within one figure and figure numbering continues correctly for subsequent figures.

Written by the indexing model from the issue text.