Add basic Wikipedia support to /fetch (#12777)

This PR extends the `/fetch` slash command with the initial support for
Wikipedia's HTML structure.

Release Notes:

- N/A

crates/html_to_markdown/src/structure/wikipedia.rs

@@ -0,0 +1,80 @@
+use crate::html_element::HtmlElement;
+use crate::markdown_writer::{MarkdownWriter, StartTagOutcome};
+use crate::HandleTag;
+
+pub struct WikipediaChromeRemover;
+
+impl HandleTag for WikipediaChromeRemover {
+    fn should_handle(&self, _tag: &str) -> bool {
+        true
+    }
+
+    fn handle_tag_start(
+        &mut self,
+        tag: &HtmlElement,
+        _writer: &mut MarkdownWriter,
+    ) -> StartTagOutcome {
+        match tag.tag.as_str() {
+            "head" | "script" | "style" | "nav" => return StartTagOutcome::Skip,
+            "sup" => {
+                if tag.has_class("reference") {
+                    return StartTagOutcome::Skip;
+                }
+            }
+            "div" | "span" | "a" => {
+                if tag.attr("id").as_deref() == Some("p-lang-btn") {
+                    return StartTagOutcome::Skip;
+                }
+
+                if tag.attr("id").as_deref() == Some("p-search") {
+                    return StartTagOutcome::Skip;
+                }
+
+                let classes_to_skip = ["mw-editsection", "mw-jump-link"];
+                if tag.has_any_classes(&classes_to_skip) {
+                    return StartTagOutcome::Skip;
+                }
+            }
+            _ => {}
+        }
+
+        StartTagOutcome::Continue
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use indoc::indoc;
+    use pretty_assertions::assert_eq;
+
+    use crate::{convert_html_to_markdown, markdown};
+
+    use super::*;
+
+    fn wikipedia_handlers() -> Vec<Box<dyn HandleTag>> {
+        vec![
+            Box::new(markdown::ParagraphHandler),
+            Box::new(markdown::HeadingHandler),
+            Box::new(markdown::ListHandler),
+            Box::new(markdown::StyledTextHandler),
+            Box::new(WikipediaChromeRemover),
+        ]
+    }
+
+    #[test]
+    fn test_citation_references_get_removed() {
+        let html = indoc! {r##"
+            <p>Rust began as a personal project in 2006 by <a href="/wiki/Mozilla" title="Mozilla">Mozilla</a> Research employee Graydon Hoare.<sup id="cite_ref-MITTechReview_23-0" class="reference"><a href="#cite_note-MITTechReview-23">[20]</a></sup> Mozilla began sponsoring the project in 2009 as a part of the ongoing development of an experimental <a href="/wiki/Browser_engine" title="Browser engine">browser engine</a> called <a href="/wiki/Servo_(software)" title="Servo (software)">Servo</a>,<sup id="cite_ref-infoq2012_24-0" class="reference"><a href="#cite_note-infoq2012-24">[21]</a></sup> which was officially announced by Mozilla in 2010.<sup id="cite_ref-MattAsay_25-0" class="reference"><a href="#cite_note-MattAsay-25">[22]</a></sup><sup id="cite_ref-26" class="reference"><a href="#cite_note-26">[23]</a></sup> Rust's memory and ownership system was influenced by <a href="/wiki/Region-based_memory_management" title="Region-based memory management">region-based memory management</a> in languages such as <a href="/wiki/Cyclone_(programming_language)" title="Cyclone (programming language)">Cyclone</a> and ML Kit.<sup id="cite_ref-influences_8-13" class="reference"><a href="#cite_note-influences-8">[5]</a></sup>
+            </p>
+        "##};
+        let expected = indoc! {"
+            Rust began as a personal project in 2006 by Mozilla Research employee Graydon Hoare.  Mozilla began sponsoring the project in 2009 as a part of the ongoing development of an experimental browser engine called Servo,  which was officially announced by Mozilla in 2010.  Rust's memory and ownership system was influenced by region-based memory management in languages such as Cyclone and ML Kit.
+        "}
+        .trim();
+
+        assert_eq!(
+            convert_html_to_markdown(html.as_bytes(), wikipedia_handlers()).unwrap(),
+            expected
+        )
+    }
+}