FEATURE: Allow rowspan and colspan attributes on HTML tables (#20973)

Augment the `allowList` for HTML tables to allow the `rowspan` and
`colspan` attributes on `th` and `td` elements.

app/assets/javascripts/discourse-markdown-it/src/features/table.js

@@ -34,7 +34,11 @@ export function setup(helper) {
     "thead",
     "tr",
     "th",
+    "th[colspan]",
+    "th[rowspan]",
     "td",
+    "td[colspan]",
+    "td[rowspan]",
     "div.md-table",
   ]);
 }

app/assets/javascripts/discourse/tests/unit/lib/sanitizer-test.js

@@ -157,6 +157,11 @@ module("Unit | Utility | sanitizer", function (hooks) {
       `<div data-value="<something>" data-html-value="<something>"></div>`,
       `<div data-value="&lt;something&gt;"></div>`
     );
+
+    cooked(
+      '<table><tr><th rowspan="2">a</th><th colspan="3">b</th><td rowspan="4">c</td><td colspan="5">d</td><td class="fa-spin">e</td></tr></table>',
+      '<table><tr><th rowspan="2">a</th><th colspan="3">b</th><td rowspan="4">c</td><td colspan="5">d</td><td>e</td></tr></table>'
+    );
   });
 
   test("ids on headings", function (assert) {