Previously we initialized with 'partial' config in the initialize handler and then fetched the proper per-workspace folder config in the initialized handler. The problem is textDocument/didOpen notifications arrive in between these, and it leads to diagnostics requests being started and then cancelled immediately. Also the init sequence is weirdly split between them, so for example the config tree walk doesn't take into account per-workspace folder enable settings on startup.

This unifies the init sequence into initialized and uses a token to prevent other request/notification handlers from running until it's complete. Also no longer send a diagnostics request on startup. Some tests which were subtly depending on this have been rewritten, but it all works in practice. Removes LspNpmConfigHash. It shouldn't be necessary since config changes are infrequent.

The token is a hack which is only required because the LSP spec doesn't allow workspace/configuration requests during initialize, which IMO it absolutely should. See microsoft/language-server-protocol#567 (comment).