Ignore tokens that were not created via WorkDoneProgressCreate

With the new version of rust-analyzer, we were seeing stray `WorkDoneProgress::End`
messages that create an imbalance in the `pending_diagnostic_updates` that never
resolves. This was causing the diagnostic status bar item to never update because
we wouldn't emit `DiskBasedDiagnosticsStarted` nor `DiskBasedDiagnosticsFinished`.

This commit fixes the above situation by only acknowledging progress report for tokens
that have explicitly been created via the `WorkDoneProgressCreate` request, as stated
by the protocol.

In addition to that, we are replacing the `pending_diagnostic_updates: isize` with
a `has_pending_diagnostic_updates: bool`. We added it at some point to prevent a similar
issue where we would observe begin/end reports in a seemingly random order, which would cause
us to permanently display a `checking...` message in the status bar. I believe this commit
fixes that as well because the `isize` was just a less general solution for the same
underlying issue. As the protocol states: "the token provided in the create request should
only be used once (e.g. only one begin, many report and one end notification should be sent
to it)."

crates/collab/src/integration_tests.rs

@@ -2995,6 +2995,7 @@ async fn test_language_server_statuses(
         .unwrap();
 
     let fake_language_server = fake_language_servers.next().await.unwrap();
+    fake_language_server.start_progress("the-token").await;
     fake_language_server.notify::<lsp::notification::Progress>(lsp::ProgressParams {
         token: lsp::NumberOrString::String("the-token".to_string()),
         value: lsp::ProgressParamsValue::WorkDone(lsp::WorkDoneProgress::Report(