Implement the LSP Starting Point Runtime Functionality

[iamrecursion]

Summary

As described in #392, it's super important to get a working subset of the LSP as soon as possible. The file operations in this subset require support in the runtime.

Value

We will have a fully working langauge server pipeline for this set of operations that includes the runtime responding properly to these changes.

Specification

• Determine how to swap between on-disk and in-memory file sources seamlessly in the interpreter.
• Implement the runtime components for the following LSP operations.
  • Text Synchronisation: didOpen
  • Text Synchronisation: didChange
  • Text Synchronisation: willSaveWaitUntil
  • Text Synchronisation: didSave
  • Text Synchronisation: didClose
• Implement tests for this functionality with a mixture of 'open' and on-disk sources.
• Implement runtime hooks to allow it to be informed of file creations and deletions from the language server's project root watching.

Acceptance Criteria & Test Cases

• The runtime has support for the required operations.