[clang] [clang-format] Separate License text and include blocks (PR #77918)

[Björn Schäpers via cfe-commits]

HazardyKnusperkeks wrote:

> > I think splitting the two features would be better.
> 
> I'm going to close this MR and create two new ones.
> 
> > Also please add a note to the changelog.
> 
> Where can I find the changelog?

`clang/docs/ReleaseNotes.rst`

https://github.com/llvm/llvm-project/pull/77918