[notification] Revise integration of user messages

[AlexTugarev]

Showing messages at top center can interrupt the user a lot. It should be easier to manage the notifications, and message service clients should have more options.

These points would be useful:

• timeout option to hide a message if no further action is required (covered by [notification] Auto-dismiss #1081).
• hide with Esc if no further action is required.
• MessageService clients should be able to dismiss a message.
• MessageService clients should be able to update the message, e.g. with progress.
• statusbar item with a counter for messages in inbox.
• button to reveal hidden messages in inbox.
• move container for notifications to a less distracting area.

Some inspiration:

[akosyakov]

Please add notificationFocus and notificationCenterVisible when context keys after implementing it, see definitions here: https://code.visualstudio.com/docs/getstarted/keybindings#_when-clause-contexts

[AndrienkoAleksandr]

It would be really nice to align notification message ui with VSCode.

[AlexTugarev]

@AndrienkoAleksandr, indeed. I’m preparing a PR.

[AlexTugarev]

related: #5635

[vince-fugnitto]

@AlexTugarev do you still plan on working on the PR?

As a POC, I attempted to first move the notifications to the bottom-right, and then update the styling:

There are a few updates to make:

• fix the transition (get a fluid animation when opening messages)
• fix the text wrap
• make messages smaller
• fix the buttons (they should look more like vscode and not take up the whole height of a notification
• allow for additional actions (almost like toolbar items).

[AlexTugarev]

Thanks @vince-fugnitto! I started working on this recently and going to push the WIP shortly. Happy to add you as reviewer.

[vince-fugnitto]

@AlexTugarev I'm excited to see what you come up with :)