[ty] Swap `detail` and `description` fields for `CompletionItemLabelDetails`

This seems to be more consistent with how other LSPs work (like
`rust-analyzer`), and also I think is more consistent with how
`CompletionItem.detail` is itself rendered. Namely, in VS Code, it
is right-aligned. And it's also where we put the type signature.
But `CompletionItemLabelDetails.detail` is left-aligned where as
`CompletionItemLabelDetails.description` is right-aligned. So let's
swap them such that type signatures go in the latter and not the
former.

This also adds a space before the module name and contextualizes
it with `(import <name>)` to help aide the end user in figuring out
selecting the completion will do.

Fixes #1200

crates/ty_server/src/server/api/requests/completion.rs

@@ -87,8 +87,8 @@ impl BackgroundDocumentRequestHandler for CompletionRequestHandler {
                     sort_text: Some(format!("{i:-max_index_len$}")),
                     detail: type_display.clone(),
                     label_details: Some(CompletionItemLabelDetails {
-                        detail: type_display,
-                        description: comp.module_name.map(ToString::to_string),
+                        detail: comp.module_name.map(|name| format!(" (import {name})")),
+                        description: type_display,
                     }),
                     insert_text: comp.insert.map(String::from),
                     additional_text_edits: import_edit.map(|edit| vec![edit]),