Update documentation images to use the 4.6 'Modern' theme

[RespiteFromReality]

I'm interested in contributing updated images with the new passivestar theme for the docs (and contrib docs), but wanted to know a few things first:

1. Is there even interest in me doing this rn?
2. Is the theme still getting any major changes?
3. Is anyone already working on this? (didn't find an issue)
4. To what degree should this be split up.

[AThousandShips]

I don't know that an update of all screenshots is critical, especially for outdated pages, and I'd say each tutorial or page should be evaluated and generally updated if needed at the same time so that the screenshots aren't updated unnecessarily if the tutorial ends up being rewritten anyway

However this, just like godotengine/godot#112495 should wait until the theme is fully finalized regardless

[skyace65]

I would say that we should be trying to update everything, I think when images don't match what the UI looks like now it can easily scare users into worrying if a page is up to date and will work or not. However, I do not think we should be updating images for the sake of updating until Beta when there's the feature freeze. If a new feature gets added that requires new/updated images then take screenshots of the editor as it is at the time, but everything else can wait.

[AThousandShips]

We will have a decision and an update from the production team when the theme is considered finalized, at the same time as we start making promotional images for the release