extension: Add support for labelDetails for LSP completions (#20144)

Closes #14278


be7336e92a/src/completion.rs (L419-L429)


be7336e92a/src/completion.rs (L555-L572)


Release Notes:

- N/A

---------

Co-authored-by: Marshall Bowers <elliott.codes@gmail.com>

crates/extension_api/wit/since_v0.2.0/lsp.wit

@@ -2,6 +2,7 @@ interface lsp {
     /// An LSP completion.
     record completion {
         label: string,
+        label-details: option<completion-label-details>,
         detail: option<string>,
         kind: option<completion-kind>,
         insert-text-format: option<insert-text-format>,
@@ -37,6 +38,12 @@ interface lsp {
         other(s32),
     }
 
+    /// Label details for an LSP completion.
+    record completion-label-details {
+        detail: option<string>,
+        description: option<string>,
+    }
+
     /// Defines how to interpret the insert text in a completion item.
     variant insert-text-format {
         plain-text,