parse table cell spans in cmark and use the information

[QuietMisdreavus]

Bug/issue #, if applicable: rdar://98017807

Summary

This PR adds support for swift-cmark's new table row- and column-spanning syntax and enables it by default. (A syntax overview is written up in the linked PR's description.) The spanning values are exposed as properties on the Table.Cell struct, with the following semantics:

• A value of 1 is the default, indicating that the cell is not spanning over other cells in that dimension.
• A value of 0 indicates that the cell is being spanned over by another cell in that dimension, and thus should be omitted when rendering HTML.
• A value greater than 1 indicates that the cell is spanning over that number of rows or columns.

Support has been added in Swift-Markdown's Markdown reformatter and its debug tree representation to properly process the new information.

Dependencies

swiftlang/swift-cmark#46 (already merged)

Testing

Use the following sample Markdown table, showcasing the new syntax:

| one | two | three |
| --- | --- | ----- |
| big      || small |
| ^        || small |

Steps:

1. swift run markdown-tool dump-tree test.md
2. Compare the output against the following dump:

Document
└─ Table alignments: |-|-|-|
   ├─ Head
   │  ├─ Cell
   │  │  └─ Text "one"
   │  ├─ Cell
   │  │  └─ Text "two"
   │  └─ Cell
   │     └─ Text "three"
   └─ Body
      ├─ Row
      │  ├─ Cell colspan: 2 rowspan: 2
      │  │  └─ Text "big"
      │  ├─ Cell colspan: 0
      │  └─ Cell
      │     └─ Text "small"
      └─ Row
         ├─ Cell colspan: 2 rowspan: 0
         ├─ Cell colspan: 0
         └─ Cell
            └─ Text "small"

Checklist

Make sure you check off the following items. If they cannot be completed, provide a reason.

• Added tests
• Ran the ./bin/test script and it succeeded
• Updated documentation if necessary

[QuietMisdreavus]

@swift-ci Please test

[daniel-grumberg]

�Should this logic be refactored?

[QuietMisdreavus]

Good idea! Just pushed up a new commit combining the logic.

[QuietMisdreavus]

@swift-ci Please test