docs: Add events import in space shooter tutorial step_2

[TravisC671]

DragUpdateInfo is included in the events package but is not in the docs.

Description

When following the shooter tutorial I had issues cause the DragUpdateInfo was undefined. upon further investigation I found that it was in the event import instead

Checklist

• [x] I have followed the Contributor Guide when preparing my PR.
• [ ] I have updated/added tests for ALL new/updated/fixed functionality.
• [x] I have updated/added relevant documentation in docs and added dartdoc comments with ///.
• [x] I have updated/added relevant examples in examples or docs.

Breaking Change?

• [ ] Yes, this PR is a breaking change.
• [x] No, this PR is not a breaking change.

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