[llvm] [mlir] [LLVM][MLIR] Move LSP server support library from MLIR into LLVM (PR #157885)

[Michał Górny via llvm-commits]

mgorny wrote:

Oh! I was looking for an actual `foo.pdll`, and to be honest my first thought is that the file got moved and the tests can't find it anymore.

Yeah, it's weird. I've checked twice, but I'll check one more time, just in case.

https://github.com/llvm/llvm-project/pull/157885