Merge `initialize` and `initializeData`

[davidscn]

Main changes of this PR

Related to precice/precice#1366

Author's checklist

• [ ] I used the pre-commit hook and used pre-commit run --all to apply all available hooks.
• [ ] I added a test to cover the proposed changes in our test suite.
• [ ] I updated the documentation in docs/README.md.
• [ ] I updated potential breaking changes in the tutorial precice/tutorials/aste-turbine.