initialize: implement serverInfo (LSP 3.15.0)

Return serverInfo for an initialize request. This helps clients to
identify ccls even when they just connect to a TCP port and allows them
to easily implement server specific functionalities like $ccls/navigate.

src/messages/initialize.cc

@@ -110,12 +110,6 @@ REFLECT_STRUCT(ServerCap, textDocumentSync, hoverProvider, completionProvider,
                documentLinkProvider, foldingRangeProvider,
                executeCommandProvider, workspace);
 
-struct ServerInfo {
-  const char *name = "ccls";
-  const char *version = CCLS_VERSION;
-};
-REFLECT_STRUCT(ServerInfo, name, version);
-
 struct DynamicReg {
   bool dynamicRegistration = false;
 };
@@ -227,8 +221,12 @@ REFLECT_STRUCT(InitializeParam, rootUri, capabilities, trace, workspaceFolders);
 
 struct InitializeResult {
   ServerCap capabilities;
-  ServerInfo serverInfo;
+  struct ServerInfo {
+    const char *name = "ccls";
+    const char *version = CCLS_VERSION;
+  } serverInfo;
 };
+REFLECT_STRUCT(InitializeResult::ServerInfo, name, version);
 REFLECT_STRUCT(InitializeResult, capabilities, serverInfo);
 
 struct FileSystemWatcher {