[clangd] Move function body to out-of-line: unnamed class method incorrect moving

The refactoring !!Move function body to out-of-line!! produces incorrect code for methods of unnamed classes.
For this simple example
  // foo.h
  struct Foo {
    struct {
      void f^oo() {}
    } Bar;
  };

the refactoring generates code:
  // foo.cpp
  void Foo::(unnamed struct at D:\test\foo.h:2:3)foo() {}

Outplace definition for methods of unnamed classes is meaningless. The patch disables it.

Reviewed By: kadircet

Differential Revision: https://reviews.llvm.org/D143638