[clang] [clang-tools-extra] [lldb] [llvm] [mlir] [NFC] Fix typos 'seperate' -> 'separate' (PR #144368)

[Baranov Victor via llvm-commits]

vbvictor wrote:

Hi, could you rebase on fresh main and fix conflicts (should be easy).
After that, could be merged

https://github.com/llvm/llvm-project/pull/144368