manual annotations in preparation of natural inference rollout in xplat/js

Summary:
X-link: react/react-native#51487

The Flow team is improving the way Flow infers type for primitive literals. This diff prepares the codebase for the new behavior by adding type annotations, or annotations of the form `'abc' as const`.

Changelog: [internal]

Reviewed By: SamChou19815

Differential Revision: D75114156

fbshipit-source-id: e3175af85cdd2388c3b45af4beb314f334e3f9b5

Author: panagosg7

packages/buck-worker-tool/src/worker-tool.js

@@ -181,8 +181,8 @@ function handshakeResponse(message: IncomingMessage) {
 
   return {
     id: message.id,
-    type: 'handshake',
-    protocol_version: '0',
+    type: 'handshake' as const,
+    protocol_version: '0' as const,
     capabilities: ([]: []),
   };
 }
@@ -281,13 +281,17 @@ function shouldDebugCommand(argsString: string) {
 }
 
 const error = (id: number, exitCode: number) => ({
-  type: 'error',
+  type: 'error' as const,
   id,
   exit_code: exitCode,
 });
 const unknownMessage = (id: number) => error(id, 1);
 const invalidMessage = (id: number) => error(id, 2);
 const commandError = (id: number) => error(id, 3);
-const success = (id: number) => ({type: 'result', id, exit_code: 0});
+const success = (id: number) => ({
+  type: 'result' as const,
+  id,
+  exit_code: 0 as const,
+});
 
 module.exports = buckWorker;

packages/metro/src/DeltaBundler/__tests__/Graph-test.js

@@ -33,6 +33,7 @@
  */
 
 import type {RequireContext} from '../../lib/contextModule';
+import type {RequireContextParams} from '../../ModuleGraph/worker/collectDependencies';
 import type {Result} from '../Graph';
 import type {
   Dependency,
@@ -81,7 +82,7 @@ const files = new CountingSet<string>();
 let transformOverrides: Map<string, TransformFn<MixedOutput>>;
 
 let graph: TestGraph;
-let options;
+let options: Options<>;
 
 let entryModule;
 let moduleFoo;
@@ -2934,7 +2935,7 @@ describe('require.context', () => {
     };
   });
 
-  const ctxParams = {
+  const ctxParams: RequireContextParams = {
     recursive: true,
     mode: 'sync',
     filter: {pattern: '.*', flags: ''},
@@ -3268,7 +3269,7 @@ describe('require.context', () => {
   });
 
   describe('when two distinct contexts match the same file', () => {
-    const narrowCtxParams = {
+    const narrowCtxParams: RequireContextParams = {
       recursive: true,
       mode: 'sync',
       filter: {pattern: '\\./narrow/.*', flags: ''},