[clangd] Make define outline code action visible

[kadircet]

Summary

This got forgotten during the process.

[merge_guards_bot]

Unit tests: pass. 61913 tests passed, 0 failed and 783 were skipped.

clang-tidy: unknown.

clang-format: pass.

Build artifacts: diff.json, clang-format.patch, CMakeCache.txt, console-log.txt, test-results.xml

clang-tools-extra/clangd/refactor/tweaks/DefineOutline.cpp

 ///   void foo();
 /// a.cc
 ///   #include "a.h"
 ///   void foo() { return; }
 class DefineOutline : public Tweak {
 public:
   const char *id() const override;
 
-  bool hidden() const override { return true; }
+  bool hidden() const override { return false; }
   Intent intent() const override { return Intent::Refactor; }
   std::string title() const override {
     return "Move function body to out-of-line.";
   }
 
   bool prepare(const Selection &Sel) override {
     // Bail out if we are not in a header file.
     // FIXME: We might want to consider moving method definitions below class