pre-suppress errors before enabling experimental.object_freeze_fix

Summary:
X-link: facebook/react-native#47141

D64152004 fixed a soundness hole in Flow's checking of frozen object types (e.g. try-Flow https://fburl.com/rmct2mf6). This diff suppresses Flow errors that appear when this fix is enabled (`experimental.object_freeze_fix` flag is set).

For most of these cases the result of `Object.freeze()` is assigned to some variable typed as a mutable type. The variable is then passed to a context where its fields can be written to. Thus changing the annotation type to a readonly version would only cause more errors downstream. So, instead, these assignments are suppressed so that the choice of using Object.freeze can be revisited.

Changelog: [internal]

Reviewed By: SamChou19815

Differential Revision: D64699992

fbshipit-source-id: 48e4376d4ed3dbda21d32cabe512e6457384994f

Author: panagosg7

packages/metro/src/index.flow.js

@@ -377,6 +377,7 @@ exports.runBuild = async (
     onComplete,
     onProgress,
     minify = true,
+    // $FlowFixMe[incompatible-variance] frozen objects are readonly
     output = outputBundle,
     out,
     platform = 'web',