Make all getTransformOptions result properties optional

Summary:
Types `getTransformOptions` as returning an object with all-optional properties.

There's no need to force Metro config authors to return a bunch of empty properties when they just want to set `transform.inlineRequires` to `true`. (Also, as a practical matter, these are already treated as optional almost everywhere, including in the React Native template.)

In an upcoming diff I will document `getTransformOptions` on the Metro website and explain what all these options are for.

Changelog:

* **[Fix]:** Make all `getTransformOptions` result properties optional

Reviewed By: huntie

Differential Revision: D41400791

fbshipit-source-id: c30dfa57ec257f079fdb4e78863fdf0dc8f968d4

Author: motiz88

packages/metro-config/src/configTypes.flow.js

@@ -40,11 +40,11 @@ export type PostProcessBundleSourcemap = ({
 };
 
 export type ExtraTransformOptions = {
-  +preloadedModules: {[path: string]: true, ...} | false,
-  +ramGroups: Array<string>,
-  +transform: {
-    +experimentalImportSupport: boolean,
-    +inlineRequires: {+blockList: {[string]: true, ...}, ...} | boolean,
+  +preloadedModules?: {[path: string]: true, ...} | false,
+  +ramGroups?: Array<string>,
+  +transform?: {
+    +experimentalImportSupport?: boolean,
+    +inlineRequires?: {+blockList: {[string]: true, ...}, ...} | boolean,
     +nonInlinedRequires?: $ReadOnlyArray<string>,
     +unstable_disableES6Transforms?: boolean,
   },

packages/metro/src/lib/transformHelpers.js

@@ -101,12 +101,12 @@ async function calcTransformerOptions(
 
   return {
     ...baseOptions,
-    inlineRequires: transform.inlineRequires || false,
-    experimentalImportSupport: transform.experimentalImportSupport || false,
+    inlineRequires: transform?.inlineRequires || false,
+    experimentalImportSupport: transform?.experimentalImportSupport || false,
     unstable_disableES6Transforms:
-      transform.unstable_disableES6Transforms || false,
+      transform?.unstable_disableES6Transforms || false,
     nonInlinedRequires:
-      transform.nonInlinedRequires || baseIgnoredInlineRequires,
+      transform?.nonInlinedRequires || baseIgnoredInlineRequires,
     type: 'module',
   };
 }