Advertise snippet_support capability to LSP

Co-Authored-By: Nathan Sobo <nathan@zed.dev>
Co-Authored-By: Max Brunsfeld <max@zed.dev>

crates/lsp/src/lsp.rs

@@ -236,6 +236,7 @@ impl LanguageServer {
                     }),
                     completion: Some(CompletionClientCapabilities {
                         completion_item: Some(CompletionItemCapability {
+                            snippet_support: Some(true),
                             resolve_support: Some(CompletionItemCapabilityResolveSupport {
                                 properties: vec!["additionalTextEdits".to_string()],
                             }),