Prevent Shift Drag Crash when single group selected

[QilongTang]

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Purpose

Per https://jira.autodesk.com/browse/DYN-5075, prevent crash when a group selected and the user still shit + left click to drag and update to display a message to the user after that or in similar situations. The original reason of the crash is that shift + left click will deselect the single node in the group first then Dynamo lost the drag target, in this case, the drag should just fail.

Declarations

Check these if you believe they are true

• The codebase is in a better state after this PR
• Is documented according to the standards
• The level of testing this PR includes is appropriate
• User facing strings, if any, are extracted into *.resx files
• All tests pass using the self-service CI.
• Snapshot of UI changes, if any.
• Changes to the API follow Semantic Versioning and are documented in the API Changes document.
• This PR modifies some build requirements and the readme is updated

Release Notes

Prevent Shift Drag Crash when single group selected

Reviewers

@DynamoDS/dynamo

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[QilongTang]

Updated message based on discussion with content developers. This is ready for review.