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/html_to_markdown.rs

@@ -1,11 +1,9 @@
 //! Provides conversion from rustdoc's HTML output to Markdown.
 
-#![deny(missing_docs)]
-
 mod html_element;
-mod markdown;
+pub mod markdown;
 mod markdown_writer;
-mod structure;
+pub mod structure;
 
 use std::io::Read;
 
@@ -19,24 +17,17 @@ use markup5ever_rcdom::RcDom;
 use crate::markdown::{
     HeadingHandler, ListHandler, ParagraphHandler, StyledTextHandler, TableHandler,
 };
-use crate::markdown_writer::{HandleTag, MarkdownWriter};
+use crate::markdown_writer::MarkdownWriter;
+
+pub use crate::markdown_writer::HandleTag;
 
 /// Converts the provided HTML to Markdown.
-pub fn convert_html_to_markdown(html: impl Read) -> Result<String> {
+pub fn convert_html_to_markdown(
+    html: impl Read,
+    handlers: Vec<Box<dyn HandleTag>>,
+) -> Result<String> {
     let dom = parse_html(html).context("failed to parse HTML")?;
 
-    let handlers: Vec<Box<dyn HandleTag>> = vec![
-        Box::new(ParagraphHandler),
-        Box::new(HeadingHandler),
-        Box::new(ListHandler),
-        Box::new(TableHandler::new()),
-        Box::new(StyledTextHandler),
-        Box::new(structure::rustdoc::RustdocChromeRemover),
-        Box::new(structure::rustdoc::RustdocHeadingHandler),
-        Box::new(structure::rustdoc::RustdocCodeHandler),
-        Box::new(structure::rustdoc::RustdocItemHandler),
-    ];
-
     let markdown_writer = MarkdownWriter::new();
     let markdown = markdown_writer
         .run(&dom.document, handlers)
@@ -47,26 +38,20 @@ pub fn convert_html_to_markdown(html: impl Read) -> Result<String> {
 
 /// Converts the provided rustdoc HTML to Markdown.
 pub fn convert_rustdoc_to_markdown(html: impl Read) -> Result<String> {
-    let dom = parse_html(html).context("failed to parse rustdoc HTML")?;
-
-    let handlers: Vec<Box<dyn HandleTag>> = vec![
-        Box::new(ParagraphHandler),
-        Box::new(HeadingHandler),
-        Box::new(ListHandler),
-        Box::new(TableHandler::new()),
-        Box::new(StyledTextHandler),
-        Box::new(structure::rustdoc::RustdocChromeRemover),
-        Box::new(structure::rustdoc::RustdocHeadingHandler),
-        Box::new(structure::rustdoc::RustdocCodeHandler),
-        Box::new(structure::rustdoc::RustdocItemHandler),
-    ];
-
-    let markdown_writer = MarkdownWriter::new();
-    let markdown = markdown_writer
-        .run(&dom.document, handlers)
-        .context("failed to convert rustdoc HTML to Markdown")?;
-
-    Ok(markdown)
+    convert_html_to_markdown(
+        html,
+        vec![
+            Box::new(ParagraphHandler),
+            Box::new(HeadingHandler),
+            Box::new(ListHandler),
+            Box::new(TableHandler::new()),
+            Box::new(StyledTextHandler),
+            Box::new(structure::rustdoc::RustdocChromeRemover),
+            Box::new(structure::rustdoc::RustdocHeadingHandler),
+            Box::new(structure::rustdoc::RustdocCodeHandler),
+            Box::new(structure::rustdoc::RustdocItemHandler),
+        ],
+    )
 }
 
 fn parse_html(mut html: impl Read) -> Result<RcDom> {