fix (Storage/FileUploader): FileUploader does not upload processed file contents in certain scenarios

Description of changes

This change fix an issue in which FileUploader does not upload the processed/modified file contents as advertised in documentation.

In current implementation, the original input file is returned as-is when hasKeyInput is false. However, the processed file contents should be returned instead regardless of the condition of hasKeyInput.

This code change fixes that and returns processed/modified file contents instead of the original.

Issue #, if available

https://github.com/aws-amplify/amplify-ui/issues/6049

Description of how you validated changes

Checklist

[x] Have read the Pull Request Guidelines
[x] PR description included
[ ] yarn test passes and tests are updated/added
[x] PR title and commit messages follow conventional commit syntax
[x] If this change should result in a version bump, changeset added (This can be done after creating the PR.) This does not apply to changes made to docs, e2e, examples, or other private packages.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

aws-amplify / amplify-ui