add support for gridtables about helix-markdown-support HOT 4 CLOSED

root[2]
├─0 heading[1]
│   │ depth: 2
│   └─0 text "Large Grid Table"
└─1 gridTable[1]
    └─0 gtHeader[3]
        ├─0 gtRow[3]
        │   ├─0 gtCell[1]
        │   │   └─0 text " A1                                                                                         "
        │   ├─1 gtCell[1]
        │   │   └─0 text " B1                                                           "
        │   └─2 gtCell[1]
        │       └─0 text " ## Lorem ipsum dolor sit amet, consectetur adipiscing elit. "
        ├─1 gtRow[3]
        │   ├─0 gtCell[15]
        │   │   ├─0  text " ## My Heading 1                                                                            "
        │   │   ├─1  text "                                                                                            "
        │   │   ├─2  text " ![](https://hlx.blob.core.windows.net/external/19c0cf25413106c81920d75078ee2ef30a55d52e7)\\ "
        │   │   ├─3  text " Lorem ipsum dolor **sit amet**, consectetur adipiscing elit. Vivamus rhoncus elit nibh,    "
        │   │   ├─4  text " sed vestibulum metus tincidunt a. _Integer_ interdum tempus consectetur. Phasellus         "
        │   │   ├─5  text " tristique auctor tortor, tincidunt semper odio blandit eu. Proin et aliquet est. Curabitur "
        │   │   ├─6  text " ac augue ornare, iaculis sem luctus, feugiat tellus.\\                                      "
        │   │   ├─7  text " 0 1 2 3 4 5 6 7 8 9 0 a b c d e f 0 1 2 3 4 5 6 7 8 9 0 a b c d e f                        "
        │   │   ├─8  text "                                                                                            "
        │   │   ├─9  text "                                                                                            "
        │   │   ├─10 text "                                                                                            "
        │   │   ├─11 text "                                                                                            "
        │   │   ├─12 text "                                                                                            "
        │   │   ├─13 text "                                                                                            "
        │   │   └─14 text "                                                                                            "
        │   ├─1 gtCell[15]
        │   │   ├─0  text " ```js                                                        "
        │   │   ├─1  text " for (const row of this.rows) {                               "
        │   │   ├─2  text "   for (let i = 0; i < row.length; i += 1) {                  "
        │   │   ├─3  text "     let col = cols[i];                                       "
        │   │   ├─4  text "     if (!col) {                                              "
        │   │   ├─5  text "       col = {};                                              "
        │   │   ├─6  text "       cols.push(col);                                        "
        │   │   ├─7  text "     }                                                        "
        │   │   ├─8  text "     const cell = row[i];                                     "
        │   │   ├─9  text "     if (cell.value) {                                        "
        │   │   ├─10 text "       col.size = Math.max(col.size || 0, cell.value.length); "
        │   │   ├─11 text "     }                                                        "
        │   │   ├─12 text "   }                                                          "
        │   │   ├─13 text " }                                                            "
        │   │   └─14 text " ```                                                          "
        │   └─2 gtCell[15]
        │       ├─0  text " > My quote                                                  "
        │       ├─1  text " >                                                           "
        │       ├─2  text " > Lorem ipsum dolor sit amet, consectetur adipiscing elit.  "
        │       ├─3  text " > Vivamus rhoncus elit nibh, sed vestibulum metus tincidunt "
        │       ├─4  text " > a.                                                        "
        │       ├─5  text "                                                             "
        │       ├─6  text " -   item one                                                "
        │       ├─7  text " -   item two                                                "
        │       ├─8  text " -   Lorem ipsum dolor sit amet, consectetur adipiscing      "
        │       ├─9  text "     elit. Vivamus rhoncus elit nibh, sed vestibulum metus   "
        │       ├─10 text "     tincidunt a.                                            "
        │       ├─11 text "                                                             "
        │       ├─12 text "                                                             "
        │       ├─13 text "                                                             "
        │       └─14 text "                                                             "
        └─2 gtRow[3]
            ├─0 gtCell[1]
            │   └─0 text " a3                                                                                         "
            ├─1 gtCell[1]
            │   └─0 text " b3                                                           "
            └─2 gtCell[1]
                └─0 text " c3                                                          "