[clang] [clang-format] Add FilesBeforeFolders option to SortIncludes (PR #208954)

[Savvas Shiakas via cfe-commits]

Shiakaron wrote:

Hi there, the code has changed significantly because I had to rebase when the `SortIncludes.Natural` option was added, and overall I am much happier with how it looks. 

> How does it work with "" and <>?

I've added a UT to cover this. When false all angle bracket includes go after quotes simply because  `"` < `<`. When true this can change because now we first check that files go before folders. So `<alpha.hpp>` will go before `"beta/x.hpp"`.

With the most recent changes I think I also addressed the 

I will try to put some time tomorrow to put together the examples I promised using `IncludeCategories`. 

https://github.com/llvm/llvm-project/pull/208954