[clangd] Send suppported codeActionKinds to the client.

[hokein]

Summary

This would make client know which codeActionKinds that clangd may
return.

VSCode will add a new entry "Refactor..." (which shows all
refactoring-kind code actions) in the right-click menu.

[ilya-biryukov]

LGTM

clang-tools-extra/clangd/ClangdLSPServer.cpp

467

NIT: a typo, s/codeActionProvide/codeActionProvider

468

s/action liveral/action literal

469

NIT: remove 'support', remove parentheses?

Otherwise we have clients supports action literal support

[hokein]

Fix the comment.

clang-tools-extra/clangd/ClangdLSPServer.cpp

void ClangdLSPServer::onInitialize(const InitializeParams &Params,
 
   // Per LSP, renameProvider can be either boolean or RenameOptions.
   // RenameOptions will be specified if the client states it supports prepare.
   llvm::json::Value RenameProvider =
       llvm::json::Object{{"prepareProvider", true}};
   if (!Params.capabilities.RenamePrepareSupport) // Only boolean allowed per LSP
     RenameProvider = true;
 
+  // Per LSP, codeActionProvide can be either boolean or CodeActionOptions.
+  // CodeActionOptions is only valid if the client supports action literal
+  // via textDocument.codeAction.codeActionLiteralSupport.
+  llvm::json::Value CodeActionProvider = true;
+  if (Params.capabilities.CodeActionStructure)
+    CodeActionProvider = llvm::json::Object{
+        {"codeActionKinds",
+         {CodeAction::QUICKFIX_KIND, CodeAction::REFACTOR_KIND,
+          CodeAction::INFO_KIND}}};
+
   llvm::json::Object Result{
       {{"capabilities",
         llvm::json::Object{
             {"textDocumentSync", (int)TextDocumentSyncKind::Incremental},
             {"documentFormattingProvider", true},
             {"documentRangeFormattingProvider", true},
             {"documentOnTypeFormattingProvider",
              llvm::json::Object{
                  {"firstTriggerCharacter", "\n"},
                  {"moreTriggerCharacter", {}},
              }},
-            {"codeActionProvider", true},
+            {"codeActionProvider", std::move(CodeActionProvider)},
             {"completionProvider",
              llvm::json::Object{
                  {"resolveProvider", false},
                  // We do extra checks for '>' and ':' in completion to only
                  // trigger on '->' and '::'.
                  {"triggerCharacters", {".", ">", ":"}},
              }},
             {"signatureHelpProvider",