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

[Jan Ječmen via llvm-commits]

JanJecmen wrote:

Somehow, we started returning errors when previously there were normal results.

Expected:
```
{
  "id": 1,
  "jsonrpc": "2.0",
  "result": {
    "output": "-Module{{.*}}PatternDecl{{.*}}Name<TestPat>{{.*}}\n"
  }
}
```

Actual:
```
{
  "error": {
    "code": -32602,
    "message": "failed to decode pdll/viewOutput request: missing value at (root).uri"
  },
  "id": 1,
  "jsonrpc": "2.0"
}
```

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