[clang] [clang-format] Enable sorting includes although formatting disabled (PR #113771)

[Martin Lambertsen via cfe-commits]

marlamb wrote:

The PR as of now is far from being complete, but before putting the effort in adding tests/documentation etc. it would be great to have some feedback, if the feature is seen worth being offered and if the proposal looks roughly acceptable. I have to admit I am not really happy about it myself, but the alternative I see (putting it into the `SortIncludes` directly, which would interfere with the `CaseSensitive` and `CaseInsensitive`) looks even less user-friendly.

https://github.com/llvm/llvm-project/pull/113771