Make getDataProvider to reduce export duplicate code

[indykoning]

Description (*)

This PR makes getDataProvider on the massaction public.
Why do we want this? To reduce unnecessary duplicate code. In the updated files you can see i've been able to remove prepareComponent.

This is because getDataProvider literally calls that when called and no dataProvider has been cached yet.

The call under there applySelectionOnTargetProvider actually calls getDataProvider as well. This means before this PR prepareComponent was always called twice during an export. Simply because we couldn't call getDataProvider and be sure prepareComponent was called.

Manual testing scenarios (*)

1. Run an export from the Magento backend with filters and selections on/off, check if it still works as expected.

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• README.md files for modified modules are updated and included in the pull request if any README.md predefined sections require an update
• All automated tests passed successfully (all builds are green)

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