lsp-test: No testing exists for prepareRename #636

The Language.LSP.Test module doesn’t export a prepareRename function for testing prepareRename requests. The test suite also doesn’t cover prepareRename.

A possible type signature is as follows:

prepareRename :: TextDocumentIdentifier -> Position -> Session (PrepareRenameResult |? Null)

This issue was suggested as a prerequisite for HLS PR #4867.