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/project.rs

@@ -68,8 +68,8 @@ use language::{
     language_settings::InlayHintKind, proto::split_operations,
 };
 use lsp::{
-    CodeActionKind, CompletionContext, CompletionItemKind, DocumentHighlightKind, LanguageServerId,
-    LanguageServerName, MessageActionItem,
+    CodeActionKind, CompletionContext, CompletionItemKind, DocumentHighlightKind, InsertTextMode,
+    LanguageServerId, LanguageServerName, MessageActionItem,
 };
 use lsp_command::*;
 use lsp_store::{CompletionDocumentation, LspFormatTarget, OpenLspBufferHandle};
@@ -392,6 +392,8 @@ pub struct Completion {
     pub source: CompletionSource,
     /// A path to an icon for this completion that is shown in the menu.
     pub icon_path: Option<SharedString>,
+    /// Whether to adjust indentation (the default) or not.
+    pub insert_text_mode: Option<InsertTextMode>,
     /// An optional callback to invoke when this completion is confirmed.
     /// Returns, whether new completions should be retriggered after the current one.
     /// If `true` is returned, the editor will show a new completion menu after this completion is confirmed.