Use NotificationRequest instead of showInformativeMessage on search

[tascodes]

Rendered

Alerts are very interruptive, and get in the way of development flow when using the search or references actions frequently.

This removes the alert and instead displays a non-interruptive notification, dismissing it 4000 ms later.

One item of note - if (!treeView.visible) always resolves to true, I assume since the newly created TreeView is not considered visible until the command is completed. Then again, a setTimeout does not affect that behavior.

[tascodes]

@apexskier Any chance you'd consider integrating this?

[github-actions[bot]]

Included in release v2.6.0