compiler: Represent pruned scopes instead of inlining

There are a few places where we want to check whether a value actually got memoized, and we currently have to infer this based on values that "should" have a scope and whether a corresponding scope actually exists. This PR adds a new ReactiveStatement variant to model a reactive scope block that was pruned for some reason, and updates all the passes that prune scopes to instead produce this new variant.

ghstack-source-id: aea6dab469
Pull Request resolved: https://github.com/facebook/react/pull/29781

compiler/packages/babel-plugin-react-compiler/src/ReactiveScopes/CodegenReactiveFunction.ts

@@ -400,6 +400,11 @@ function codegenBlockNoReset(
         }
         break;
       }
+      case "pruned-scope": {
+        const scopeBlock = codegenBlockNoReset(cx, item.instructions);
+        statements.push(...scopeBlock.body);
+        break;
+      }
       case "scope": {
         const temp = new Map(cx.temp);
         codegenReactiveScope(cx, statements, item.scope, item.instructions);