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

[Savvas Shiakas via cfe-commits]

Shiakaron wrote:

> > > While I absolutely share this sorting, it is already possible with the regexes and the priorities without any doubt or confusion.
> > 
> > 
> > @HazardyKnusperkeks I have tried to achieve this using regexes and priorities but could only go far due to the iterative nature of this sorting. This is what we have, which fails to replicate the desired logic:
> > ```
> > IncludeCategories:
> >   - Regex: '^[^/]*$'
> >     SortPriority: 0
> >   - Regex: '^[^/]*/[^/]*$'
> >     SortPriority: 1
> >   - Regex: '^[^/]*(/[^/]*){2}$'
> >     SortPriority: 2
> >   - Regex: '^[^/]*(/[^/]*){3}$'
> >     SortPriority: 3
> >   - Regex: '^[^/]*(/[^/]*){4}$'
> >     SortPriority: 4
> >   - Regex: '^[^/]*(/[^/]*){5}$'
> >     SortPriority: 5
> > ```
> > 
> > 
> >     
> >       
> >     
> > 
> >       
> >     
> > 
> >     
> >   
> > Is it possible for you to share your clang format settings? I would be so happy if this is really possible with the regexes and sort priorities
> 
> This is what I have for that priority:
> 
> ```
>   - Regex:           '^"\.\./\.\./.*'
>     Priority:        10
>     SortPriority:    14
>     CaseSensitive:   false
>   - Regex:           '^"\.\./[^/]+/.*'
>     Priority:        10
>     SortPriority:    13
>     CaseSensitive:   false
>   - Regex:           '^"\.\./.*'
>     Priority:        10
>     SortPriority:    12
>     CaseSensitive:   false
>   - Regex:           '^".*/'
>     Priority:        10
>     SortPriority:    11
>     CaseSensitive:   false
>   - Regex:           '^".*'
>     Priority:        10
>     SortPriority:    10
>     CaseSensitive:   false
> ```
> 
> Yeah of course that is repetitive, depending on how many levels you want to support. But on any given code base the levels are finite, you could even write a small script to generate the needed configuration.

@HazardyKnusperkeks Ok it seems we have gone for the same sort of approach, just a bit different since we don't use `../` in our paths. 

However, I would still argue the sorting I am going for in this change is substantially different and it cannot be achieved using the `IncludeCategories`, because, irrespective on the levels in your project, you can have an "unlimited" number of categories. I will come back with a concrete example that will make my case much more clearer.

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