Pre-suppress unused-promise lint errors in xplat/js (#36590)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/36590

Pre-suppress unused-promise lint errors in xplat/js. The next diff enables the lint.

See https://flow.org/en/docs/linting/rule-reference/#toc-unused-promise for more details.

Changelog: [Internal]

drop-conflicts
bypass-lint

Reviewed By: pieterv

Differential Revision: D43967290

fbshipit-source-id: f36242a732dbc18bf7482adfb46ca2b77e1b1493

IntegrationTests/PromiseTest.js

@@ -22,6 +22,7 @@ class PromiseTest extends React.Component<{...}> {
   shouldThrowAsync: boolean = false;
 
   componentDidMount() {
+    // $FlowFixMe[unused-promise]
     Promise.all([
       this.testShouldResolve(),
       this.testShouldReject(),