make LRU cache configurable

editors/code/src/config.ts

@@ -19,6 +19,7 @@ export class Config {
     public enableEnhancedTyping = true;
     public raLspServerPath = RA_LSP_DEBUG || 'ra_lsp_server';
     public showWorkspaceLoadedNotification = true;
+    public lruCapacity: null | number = null;
     public cargoWatchOptions: CargoWatchOptions = {
         enableOnStartup: 'ask',
         trace: 'off',
@@ -109,5 +110,8 @@ export class Config {
                 ''
             );
         }
+        if (config.has('lruCapacity')) {
+            this.lruCapacity = config.get('lruCapacity') as number;
+        }
     }
 }