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

[Jan Ječmen via llvm-commits]

JanJecmen wrote:

It seems to me there is no actual file foo.pdll, there is instead a message that tells the server that a file foo.pdll was open and what the contents are:
```
{"jsonrpc":"2.0","method":"textDocument/didOpen","params":{"textDocument":{
  "uri":"test:///foo.pdll",
  "languageId":"pdll",
  "version":1,
  "text":"Pattern TestPat => erase op<test.op>;"
}}}
```

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