Merge the "show notifications" and "silence notifications" button

[mieldepoche]

Describe the project you are working on

prototypes

Describe the problem or limitation you are having in your project

https://github.com/godotengine/godot-proposals/assets/71937306/1eada3ae-e5a8-454b-b51b-5706ab7fd766

The button to show the notifications and the one to dismiss them are 2 different buttons.

Describe the feature / enhancement and how it helps to overcome the problem or limitation

• The show notifications button would now toggle the status while toggling between the two existing icons.
• The current notification dismiss button would be removed and the notification stack would be padded to the right.

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

watch the video above and imagine my clicks hiding the notifications

If this enhancement will not be used often, can it be worked around with a few lines of script?

I don't know how many people actually have the notifications turned on, but since it's there already might as well make it less janky.

Is there a reason why this should be core and not an add-on in the asset library?

it's core already