[clang-format] Support indentation of preprocessor directives to level of surrounding code

Please support indentation of preprocessor directives to level of surrounding code.

I want
```cpp
int main()
{

#warning This is a test!

while (true)
{
DoThingOne();

#ifdef MACRO_A
DoThingThree();
#endif
}

return 0;
}

```
to to be formatted as
```cpp
int main()
{

#warning This is a test!

while (true)
{
DoThingOne();

#ifdef MACRO_A
DoThingThree();
#endif
}

return 0;
}
```

Related: https://www.reddit.com/r/cpp_questions/comments/102vlmu/indent_macros_with_clang_format/

No source file or test is named. Start by locating clang-format's handling of preprocessor directives, then use the issue's C++ examples as the acceptance cases: directives should align with their surrounding code level while nested body statements retain their indentation.

Written by the indexing model from the issue text.