Previously we used our own homespun formatting. But this
produces over-long lines that aren't ideal for diffs in tests.
Easier to use something off-the-shelf and standard.
Closes#7580.
Performance is slower by about a factor of 10, but this isn't
really a problem because native isn't suitable as a serialization
format. (For serialization you should use json, because the reader
is so much faster than native.)
- Writers.Native is now adapted to the new Table type.
- Inline captions should now be conditionally wrapped in a Plain, not
a Para block.
- The toLegacyTable function now lives in Writers.Shared.
Babel result blocks can have block attributes like captions and names.
Result blocks with attributes were not recognized and were parsed as
normal blocks without attributes.
Fixes: #3706
