[CHORE] Remove github.com/yuin/goldmark-meta

- Remove a unused dependency. This dependency was added to handle YAML
'frontmatter' meta, parsing them and converting them to a table or
details in the resulting HTML. As can be read in the issue that reported
the behavior of YAML frontmatter being rendered literally,
https://github.com/go-gitea/gitea/issues/5377.
- It's an unused dependency as the codebase since then moved on to do this YAML
parsing and rendering on their own, this was implemented in
812cfd0ad9.
- Adds unit tests that was related to this functionality, to proof the
codebase already handles this and to prevent regressions.

modules/markup/markdown/markdown_test.go

@@ -1210,3 +1210,127 @@ func TestCustomMarkdownURL(t *testing.T) {
 	test("[test](abp)",
 		`<p><a href="http://localhost:3000/gogits/gogs/src/branch/main/abp" rel="nofollow">test</a></p>`)
 }
+
+func TestYAMLMeta(t *testing.T) {
+	setting.AppURL = AppURL
+
+	test := func(input, expected string) {
+		buffer, err := markdown.RenderString(&markup.RenderContext{
+			Ctx: git.DefaultContext,
+		}, input)
+		assert.NoError(t, err)
+		assert.Equal(t, strings.TrimSpace(expected), strings.TrimSpace(string(buffer)))
+	}
+
+	test(`---
+include_toc: true
+---
+## Header`,
+		`<details><summary><i class="icon table"></i></summary><table>
+<thead>
+<tr>
+<th>include_toc</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+<td>true</td>
+</tr>
+</tbody>
+</table>
+</details><details><summary>toc</summary><ul>
+<li>
+<a href="#user-content-header" rel="nofollow">Header</a></li>
+</ul>
+</details><h2 id="user-content-header">Header</h2>`)
+
+	test(`---
+key: value
+---`,
+		`<details><summary><i class="icon table"></i></summary><table>
+<thead>
+<tr>
+<th>key</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+<td>value</td>
+</tr>
+</tbody>
+</table>
+</details>`)
+
+	test("---\n---\n",
+		`<hr/>
+<hr/>`)
+
+	test(`---
+gitea:
+  details_icon: smiley
+  include_toc: true
+---
+# Another header`,
+		`<details><summary><i class="icon smiley"></i></summary><table>
+<thead>
+<tr>
+<th>gitea</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+<td><table>
+<thead>
+<tr>
+<th>details_icon</th>
+<th>include_toc</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+<td>smiley</td>
+<td>true</td>
+</tr>
+</tbody>
+</table>
+</td>
+</tr>
+</tbody>
+</table>
+</details><details><summary>toc</summary><ul>
+<li>
+<a href="#user-content-another-header" rel="nofollow">Another header</a></li>
+</ul>
+</details><h1 id="user-content-another-header">Another header</h1>`)
+
+	test(`---
+gitea:
+  meta: table
+key: value
+---`, `<table>
+<thead>
+<tr>
+<th>gitea</th>
+<th>key</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+<td><table>
+<thead>
+<tr>
+<th>meta</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+<td>table</td>
+</tr>
+</tbody>
+</table>
+</td>
+<td>value</td>
+</tr>
+</tbody>
+</table>`)
+}