[Feature] Update InAppNotification style

[ismaelestalayo]

Describe the problem this feature would solve

The visual style of InAppNotification should be updated to match that of the InfoBar.

Current style of the InAppNotification:

Current style of InfoBar (with hover over Close button):

Describe the solution

My proposal

• Removes the border from the notification.
• Lowers the fontsize to match the one from InfoBar
• Brings the background color of the notification from InfoBar.
• Applies a similar background change to the Close button on hover (and has rounded corners as well), and moves it to the top.
• Removes the foreground change on the Close button on hover.

Describe alternatives you've considered

Currently I was using InAppNotification and I was playing with the idea of moving to either TeachingTooltip or InfoBar (although the latter is not meant for the kind of "temporal notifications" I want to warn the user about).

Hello, 'ismaelestalayo! Thanks for submitting a new feature request. I've automatically added a vote 👍 reaction to help get things started. Other community members can vote to help us prioritize this feature in the future!

[Kyaa-dost]

Thanks, @ismaelestalayo for filing an issue and submitting a PR ❤️

[michael-hawker]

Thanks @ismaelestalayo for taking a look at this! I was originally thinking we'd just swap the guts of the control out for an InfoBar directly and hook-up things to keep the same outer API for the InAppNotification, but I like your simple updates to the style as an intermediary step. 😊

This means we can take your PR for 7.0, and then worry about a larger overhaul later. Maybe it's something we just do for our WinUI based branch as an experiment first or something. We can file a different issue to track future work though.