Refactor markup render system (#32533)

Remove unmaintainable sanitizer rules. No need to add special "class"
regexp rules anymore, use RenderInternal.SafeAttr instead, more details
(and examples) are in the tests

modules/markup/markdown/markdown_test.go

@@ -1051,3 +1051,17 @@ func TestAttention(t *testing.T) {
 	// legacy GitHub style
 	test(`> **warning**`, renderAttention("warning", "octicon-alert")+"\n</blockquote>")
 }
+
+func BenchmarkSpecializedMarkdown(b *testing.B) {
+	// 240856	      4719 ns/op
+	for i := 0; i < b.N; i++ {
+		markdown.SpecializedMarkdown(&markup.RenderContext{})
+	}
+}
+
+func BenchmarkMarkdownRender(b *testing.B) {
+	// 23202	     50840 ns/op
+	for i := 0; i < b.N; i++ {
+		_, _ = markdown.RenderString(&markup.RenderContext{Ctx: context.Background()}, "https://example.com\n- a\n- b\n")
+	}
+}