Tell language servers that Helix can request formatting (#11064)

Without providing the formatting capability, the language server might not advertise its ability to format in return, causing the :format command to be broken.

helix-lsp/src/client.rs

@@ -616,6 +616,9 @@ pub(crate) async fn initialize(&self, enable_snippets: bool) -> Result<lsp::Init
                         prepare_support_default_behavior: None,
                         honors_change_annotations: Some(false),
                     }),
+                    formatting: Some(lsp::DocumentFormattingClientCapabilities {
+                        dynamic_registration: Some(false),
+                    }),
                     code_action: Some(lsp::CodeActionClientCapabilities {
                         code_action_literal_support: Some(lsp::CodeActionLiteralSupport {
                             code_action_kind: lsp::CodeActionKindLiteralSupport {