edit prediction: Context debug view (#38435)

Adds a `dev: open edit prediction context` action that opens a new
workspace pane that displays the excerpts and snippets that would be
included in the edit prediction request.

Release Notes:

- N/A

---------

Co-authored-by: Bennet <bennet@zed.dev>

crates/language/src/language_registry.rs

@@ -646,6 +646,24 @@ impl LanguageRegistry {
         async move { rx.await? }
     }
 
+    pub async fn language_for_id(self: &Arc<Self>, id: LanguageId) -> Result<Arc<Language>> {
+        let available_language = {
+            let state = self.state.read();
+
+            let Some(available_language) = state
+                .available_languages
+                .iter()
+                .find(|lang| lang.id == id)
+                .cloned()
+            else {
+                anyhow::bail!(LanguageNotFound);
+            };
+            available_language
+        };
+
+        self.load_language(&available_language).await?
+    }
+
     pub fn language_name_for_extension(self: &Arc<Self>, extension: &str) -> Option<LanguageName> {
         self.state.try_read().and_then(|state| {
             state