[clang-include-cleaner] unnecessary include suggested when including fully contained header

[firewave]

test.h

#include <string>

struct S
{
    const std::string& str() const;
    std::string mStr;
};

test.cpp

#include "test.h"

const std::string& S::str() const
{
    return mStr;
}

$ clang-include-cleaner --print=changes test.cpp
[...]
+ <string>

[llvmbot]

@llvm/issue-subscribers-clang-include-cleaner

Author: Oliver Stöneberg (firewave)

test.h ```cpp #include <string>

struct S
{
const std::string& str() const;
std::string mStr;
};

test.cpp
```cpp
#include "test.h"

const std::string& S::str() const
{
    return mStr;
}

$ clang-include-cleaner --print=changes test.cpp
[...]
+ <string>