feat: support HTML table tags in doc comments

Previously, an HTML table in a doc comment triggered:

  warning: HTML <table> tag not followed by pure text

and then a fatal error: the existing HTML start-tag handler could only
gather pure text between a tag and its matching end tag. The doc-comment
extractor now recognizes `<table>`/`<tr>`/`<th>`/`<td>` and populates
the existing `TableBlock`/`TableRow`/`TableCell` metadata.

The HTML and Adoc generators each gain a doc/block/table partial. The
Adoc output uses the `[%header]` table attribute when the first row is a
header; the HTML output emits plain `<table>`/`<tr>`/`<th>`/`<td>`. The
XML generator already serialized the metadata generically.

Not (yet?) supported:

- HTML attributes on `<table>`/`<tr>`/`<th>`/`<td>` (`align`, `colspan`,
  `rowspan`, `class`, `style`, ...). Column alignment is therefore never
  populated (`TableBlock::Alignments` is always empty) and cells cannot
  span rows or columns.
- `<caption>`, `<col>`, and `<colgroup>`.
- Block-level content inside cells (paragraphs, lists, code blocks).
  Cells currently hold only inline content.

Closes issue #1146.

Author: gennaroprota

mrdocs.rnc

@@ -726,7 +726,7 @@ grammar
         element table-row
         {
             element is-header { Bool }?,
-            element cells { TableCell }*
+            TableCell*
         }
 
     TableBlock =

share/mrdocs/addons/generator/adoc/partials/doc/block/table.adoc.hbs

@@ -0,0 +1,4 @@
+{{#if items.[0].is_header}}[%header]
+{{/if}}|===
+{{#each items}}{{#each cells}}| {{> doc/inline-container }} {{/each}}
+{{/each}}|===

share/mrdocs/addons/generator/html/partials/doc/block/table.html.hbs

@@ -0,0 +1,5 @@
+<table>
+{{#each items}}<tr>
+{{#each cells}}{{#if ../is_header}}<th>{{> doc/inline-container }}</th>{{else}}<td>{{> doc/inline-container }}</td>{{/if}}
+{{/each}}</tr>
+{{/each}}</table>