More maintainable config

Rather than eagerly converting JSON, we losslessly keep it as is, and
change the shape of user-submitted data at the last moment.

This also allows us to remove a bunch of wrong Defaults

crates/rust-analyzer/src/global_state.rs

@@ -109,7 +109,7 @@ impl GlobalState {
             Handle { handle, receiver }
         };
 
-        let analysis_host = AnalysisHost::new(config.lru_capacity);
+        let analysis_host = AnalysisHost::new(config.lru_capacity());
         let (flycheck_sender, flycheck_receiver) = unbounded();
         GlobalState {
             sender,