Refactor: Make NativeModuleAliasMap $ReadOnly

Summary:
We were using `$ReadOnly<NativeModuleAliasMap>` everywhere, so I figured we'd just make the type itself `$ReadOnly`.

Changelog: [Internal]

Reviewed By: PeteTheHeat

Differential Revision: D23645207

fbshipit-source-id: 4e018d5768f4fcfd00492def7d840a5054cb2b73

packages/react-native-codegen/src/CodegenSchema.js

@@ -267,13 +267,13 @@ export type Required<T> = $ReadOnly<{...T, nullable: false}>;
 
 export type NativeModuleSchema = $ReadOnly<{|
   // We only support aliases to Objects
-  aliases: $ReadOnly<NativeModuleAliasMap>,
+  aliases: NativeModuleAliasMap,
   properties: $ReadOnlyArray<NativeModulePropertySchema>,
 |}>;
 
-export type NativeModuleAliasMap = {
+export type NativeModuleAliasMap = $ReadOnly<{|
   [aliasName: string]: Required<NativeModuleObjectTypeAnnotation>,
-};
+|}>;
 
 export type NativeModulePropertySchema = $ReadOnly<{|
   name: string,

packages/react-native-codegen/src/parsers/flow/modules/index.js

@@ -38,7 +38,7 @@ function translateTypeAnnotation(
    */
   flowTypeAnnotation: $FlowFixMe,
   types: TypeDeclarationMap,
-  aliasMap: NativeModuleAliasMap,
+  aliasMap: {...NativeModuleAliasMap},
 ): NativeModuleTypeAnnotation {
   const {
     nullable,
@@ -306,7 +306,7 @@ function translateFunctionTypeAnnotation(
   flowFunctionTypeAnnotation: $FlowFixMe,
   types: TypeDeclarationMap,
   nullable: boolean,
-  aliasMap: NativeModuleAliasMap,
+  aliasMap: {...NativeModuleAliasMap},
 ): NativeModuleFunctionTypeAnnotation {
   const params: Array<NativeModuleMethodParamSchema> = [];
   for (const flowParam of (flowFunctionTypeAnnotation.params: $ReadOnlyArray<$FlowFixMe>)) {
@@ -367,7 +367,7 @@ function buildPropertySchema(
   // Flow type this node
   property: $FlowFixMe,
   types: TypeDeclarationMap,
-  aliasMap: NativeModuleAliasMap,
+  aliasMap: {...NativeModuleAliasMap},
 ): NativeModulePropertySchema {
   let nullable = false;
   let {key, value} = property;
@@ -422,7 +422,7 @@ function buildModuleSchema(
   return (declaration.body.properties: $ReadOnlyArray<$FlowFixMe>)
     .filter(property => property.type === 'ObjectTypeProperty')
     .map(property => {
-      const aliasMap: NativeModuleAliasMap = {};
+      const aliasMap: {...NativeModuleAliasMap} = {};
       return {
         aliasMap: aliasMap,
         propertySchema: buildPropertySchema(