[clangd] Turn on RecoveryAST for clangd by default.

[sammccall]

clang-tools-extra/clangd/tool/ClangdMain.cpp

285

Ah actually in other options, we set the default in the struct and reference it here. Can we do that here too?

[hokein]

address review comment.

clang-tools-extra/clangd/tool/ClangdMain.cpp

opt<bool> CrossFileRename{
     cat(Features),
     desc("Enable cross-file rename feature."),
     init(true),
 };
 
 opt<bool> RecoveryAST{
     "recovery-ast",
     cat(Features),
-    desc("Preserve expressions in AST for broken code (C++ only). Note that "
-         "this feature is experimental and may lead to crashes"),
-    init(false),
-    Hidden,
+    desc("Preserve expressions in AST for broken code (C++ only)."),
+    init(true),
 };
+
 opt<bool> RecoveryASTType{
     "recovery-ast-type",
     cat(Features),
     desc("Preserve the type for recovery AST. Note that "
          "this feature is experimental and may lead to crashes"),
     init(false),
     Hidden,
 };