Error autocompleting if document changes in-flight

[radeksimko]

Per LSP spec:

if a server detects a state change that invalidates the result of a request in execution the server can error these requests with ContentModified. If clients receive a ContentModified error, it generally should not show it in the UI for the end-user. Clients can resend the request if appropriate.

We might be able to leverage document versions and compare versions and the beginning and before the end of completion handler.

This is especially important when completing because the operation may be expensive and time-consuming. Getting github schema from Terraform can take around 1sec and could take much more for bigger providers, so the user (or anything outside of the editor) may continue modifying the document in the meantime which then invalidates the list of completion candidates.

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Resolving this will also allow us to block responding to a completion or formatting request until loading for the relevant root module is finished as per #218

[danieldreier]

@radeksimko am I understanding right that this is effectively blocked on #426 because with concurrency = 1 ContentModified would only be processed after the autocomplete is returned?

[radeksimko]

@danieldreier That is right, but fix is coming 🔜 - #489