Navigation: Consider animations for mobile menu

[beafialho]

Currently, the navigation block is not only buggy (see #43523) but also quite flat. The fact that it's not possible to add any animation to it, seems like a missed opportunity to enhance a website with a very simple, basic detail.

Animation in the header would already enhance the overall feel of a website. If it worked well, we could extend it to page transitions or even sections of the site. Other site builders do it and it would be nice to have these options available in Gutenberg.

This feature could simply have animation presets. Here are a few good examples.

Here's the current GB default mobile menu:

navanimation.mp4

Here's a mobile menu in another site builder with a subtle fade in from bottom:

navanimation2.mp4