Implement text/closeFile

[iamrecursion]

Summary

For text files that are able to be edited collaboratively it's very important that the language server knows which of the files are open by which clients. The text/closeFile message is what informs the LS about this.

Value

Knowing which files are open is incredibly important for the purposes of both updating clients on changes and knowing when to read files from disk or from an in-memory representation. This message ensures that the language server can retain a coherent picture of the project.

Specification

• Implement the text/closeFile message as specified in the design document.
• This should track which files are open on a per-client basis, and keep them loaded into in-memory buffers.
• Specify any errors in the design document.

Acceptance Criteria & Test Cases

• The above specification has been implemented.
• The features have been rigorously tested.