Add support for insert_text_mode of a completion (#28171)

I wanted this for CONL (https://conl.dev )'s nascent langauge server,
and it seems like most of the support was already wired up on the LSP
side, so this surfaces it into the editor.

Release Notes:

- Added support for the `insert_text_mode` field of completions from the
language server protocol.

crates/project/src/lsp_store.rs

@@ -8053,6 +8053,7 @@ impl LspStore {
                         runs: Default::default(),
                         filter_range: Default::default(),
                     },
+                    insert_text_mode: None,
                     icon_path: None,
                     confirm: None,
                 }]))),
@@ -9342,6 +9343,7 @@ async fn populate_labels_for_completions(
                     documentation,
                     old_range: completion.old_range,
                     new_text: completion.new_text,
+                    insert_text_mode: lsp_completion.insert_text_mode,
                     source: completion.source,
                     icon_path: None,
                     confirm: None,
@@ -9356,6 +9358,7 @@ async fn populate_labels_for_completions(
                     old_range: completion.old_range,
                     new_text: completion.new_text,
                     source: completion.source,
+                    insert_text_mode: None,
                     icon_path: None,
                     confirm: None,
                 });