Ensure LSP requests don't use stale data

[dfreeman]

Another bugfix for something I ran into working on typesafe reexports. This struck particularly frequently with autosuggest (for reasons that will become clear) but was actually a potential problem for any LSP request coming in immediately after an editor change.

Prior to this change, requests to the language server would use the most recently calculated transform information about open files without triggering a recalculation themselves. This nearly always worked, because following any sequence of changes with a brief cooldown, we'd interrogate the TS language service for diagnostics, which would trigger a fresh transformation of any changed modules. If a request came in during that cooldown period, though, they would operate against the version of the workspace from before the change, potentially leading to incorrect results.

This change ensures all operations go through a flow that validates the document hasn't changed since the last transform, rather than only attempts to read the file contents.