Tolerate negative colwidth values to round-trip

[Chris Fuller]

Although the documentation says that the values in a tableCell or tableHeader’s colwidth array must be positive (with a few special cases that allow 0), this is not enforced by the JSON Schema. In the editor, it seems that negative values are tolerated and preserved and that they make it through to the final HTML:

So even if the library remains strict at the API level, it should permit these values to round-trip (by bypassing validation during the parse step).

[Chris Fuller]

Apparently, this isn't needed because the ADF document actually does fail validation at a different stage of the request processing.