Added new event enum + constructor for hot runner

[eliasyishak]

Related to tracker issue:

• ☂️ package:unified_analytics implementation in flutter tool flutter/flutter#128251

PR in flutter/flutter implementing this new Event:

• Migration for HotEvent for Flutter hot runner flutter/flutter#137717

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[github-actions]

Package publishing

Package	Version	Status	Publish tag (post-merge)
package:unified_analytics	5.2.0	ready to publish	unified_analytics-v5.2.0
package:extension_discovery	2.0.1-wip	WIP (no publish necessary)
package:cli_config	0.1.2	already published at pub.dev
package:graphs	2.3.2-wip	WIP (no publish necessary)

Documentation at https://github.com/dart-lang/ecosystem/wiki/Publishing-automation.

[christopherfujino]

LGTM