Add task_display_name to GanttTaskInstance

[guan404ming]

Related Issue

#46730

How

• add the task_display_name for GanttTaskInstance
• update tests and ui usage

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• Read the Pull Request Guidelines for more information. Note: commit author/co-author name and email in commits become permanently public when merged.
• For fundamental code changes, an Airflow Improvement Proposal (AIP) is needed.
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