Update Size and anchors page for Godot 4.0

[JaviARodriguez]

Updates the "Size and anchors" reflect the changes in how anchors work. New screenshots have been included that show the new Layout Menu toolbar, as well as the changes to the anchor properties in the inspector. References to "margins" have been changed to "offsets".

Issue #5121 Documentation pages to add or update for Godot 4.0

[skyace65]

Closing this as it was superseded by #10216. That PR was more minimal in terms of re-writes so if you want to open a new PR to refine this page further please feel free to do so! And thank you for making this PR even though it wasn't merged.

One thing I would like to note if you plan to update images in the future, we're using webp as our image file format, and based on the size of your screenshots it looks like they were taken on a 4K monitor and would need to be scaled down. We have information on converting and scaling images on this page if you need it in the future.