Docx reader - support new table features

[jgm]

Add support for new table features introduced in jgm/pandoc-types#66 including table attributes (including identifier), ~rowspan, colspan~ (this was implemented in https://github.com/jgm/pandoc/commit/56b211120c62a01f8aba1c4512acfe4677d8c7d0), table head and foot, ~multiple header lines~, row headers, captions that allow block-level content and include an optional short caption.

[emdash-ie]

I'm gonna give this issue a shot now (as part of Zurihac)

[tarleb]

This will also fix #2783.

[tarleb]

Reopening, was closed by accident.

[emdash-ie]

With the work in #6512 merged, the following have been completed:

• rowspan & colspan
• multiple header lines
• partial support for block-level content in captions