[ty] add docstrings to completions based on type (#20008)

This is a fairly simple but effective way to add docstrings to like 95%
of completions from initial experimentation.

Fixes https://github.com/astral-sh/ty/issues/1036

Although ironically this approach *does not* work specifically for
`print` and I haven't looked into why.

crates/ty_wasm/src/lib.rs

@@ -421,7 +421,10 @@ impl Workspace {
             .into_iter()
             .map(|completion| Completion {
                 kind: completion.kind(&self.db).map(CompletionKind::from),
-                name: completion.name.into(),
+                name: completion.inner.name.into(),
+                documentation: completion
+                    .documentation
+                    .map(|documentation| documentation.render_plaintext()),
             })
             .collect())
     }
@@ -908,6 +911,8 @@ pub struct Completion {
     #[wasm_bindgen(getter_with_clone)]
     pub name: String,
     pub kind: Option<CompletionKind>,
+    #[wasm_bindgen(getter_with_clone)]
+    pub documentation: Option<String>,
 }
 
 #[wasm_bindgen]