Update Gridmaps page for 4.4

[skyace65]

Does what the title says. The gridmap creation process on this page is largely the same as before, but the editor has changed substantially and is now its own panel on the bottom of the editor, similar to the tilemap editor.

• All images have gone through squoosh compression
• Documents changes from Move GridMapEditor to bottom panel godot#96922 and Add ShadowCastingSetting to MeshLibrary / GridMap items godot#85443
• covers some of the issues in Updating and Improving Documentation for Gridmap Editor #10265

@Nodragem since you updated the gridmap editor any thoughts?

[tetrapod00]

Need to change ~~~~~~~~~~~~~~ to ============== at the top of the page, somehow I missed that in the big standardization.

[tetrapod00]

Only checked for grammar/style; the images look okay at a glance but I didn't follow along with the tutorial

[skyace65]

Fixed

[tetrapod00]

I think it's good as-is but I may come back later and follow the tutorial to see if that catches anything else.