Add bulk delete and mark actions to Task Instances page (#63855)

[shashbha14]

Closes #63855

Airflow 2 included multi-select bulk actions on the "Browse -> Task Instances" page. This PR reintroduces
this feature in Airflow 3.
It Adds:

• Checkboxes on each task instance row with select-all header checkbox
• ActionBar appears at bottom of page with multiple rows selected
• Bulk Mark As - Dialog to mark selected task instances as Success/Failed
• Bulk Delete - Dialog to delete selected task instances
• Row-level action buttons (Clear, Mark As, Delete) are disabled with bulk selections active

Out of scope:

• "Bulk Clear" - Requires different context and API

Test plan

• Navigate to "Browse -> Task Instances"
• Verify checkboxes are in first column
• Select multiple rows - ActionBar appears at bottom
• Click "Mark As..." - Dialog appears with Success/Failed buttons
• Click Success/Failed - Dialog allows confirmation
• Click "Delete" - Confirmation dialog appears - Delete works
• Click X in ActionBar - Selections cleared
• Individual row-level action buttons are disabled with bulk selections active