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

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seranu wrote:

> You'd have to create multiple pull requests. And if they build on each other there is no nice way of doing this on github. You can of course use this one for a change. You can also not split the work, but chances are it will take longer for the changes to land.

I created a new PR for the test refactoring at https://github.com/llvm/llvm-project/pull/78108

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