Implement workspace file/folder LSP handlers

[retailcoder]

• Implement workspace/workspaceFolders request #43
• Implement workspace/willCreateFiles notification #44
• Implement workspace/didCreateFiles notification #45
• Implement workspace/willRenameFiles notification #46
• Implement workspace/didRenameFiles notification #47
• Implement workspace/willDeleteFiles notification #48
• Implement workspace/didDeleteFiles notification #49
• Implement workspace/didChangeWatchedFiles notification #50

The handlers themselves should go under Rubberduck.Client, which should have a namespace to keep the workspace handlers together (there will be more workspace handlers to implement in future sprints). Handlers should be injected with interfaces for the services they need, so these services need to have their interfaces in the same assembly, to be implemented under Rubberduck.Server.LSP.