markdown: Make cx the last parameter to the constructor (#21487)

I noticed that `Markdown::new` didn't have the `cx` as the final
parameter, as is conventional.

This PR fixes that.

Release Notes:

- N/A

crates/markdown/src/markdown.rs

@@ -71,8 +71,8 @@ impl Markdown {
         source: String,
         style: MarkdownStyle,
         language_registry: Option<Arc<LanguageRegistry>>,
-        cx: &ViewContext<Self>,
         fallback_code_block_language: Option<String>,
+        cx: &ViewContext<Self>,
     ) -> Self {
         let focus_handle = cx.focus_handle();
         let mut this = Self {