Add 'clear' helper (#17209)

src/server/scriptInfo.ts

@@ -242,7 +242,7 @@ namespace ts.server {
                 // detach is unnecessary since we'll clean the list of containing projects anyways
                 p.removeFile(this, /*detachFromProjects*/ false);
             }
-            this.containingProjects.length = 0;
+            clear(this.containingProjects);
         }
 
         getDefaultProject() {