Change resolution/scaling defaults

[Joy-less]

The first thing I do when making any project in Godot is the following:

• Change display/window/size/ viewport_width/viewport_height to 640x360. The default of 1152x648 is 60% of the screen in 1920x1080, which gives you more space to work with, but it doesn't upscale cleanly into any common resolutions. 640x360 cleanly upscales into 720p (HD-ready), 1080p (HD), 1440p (QHD) and 2160p (UHD).
• Change display/window/stretch/mode to canvas_items and display/window/stretch/aspect to expand. This allows the window to be automatically scaled to any aspect ratio without letterboxing. The default doesn't upscale at all and keeps the content in the top-left which is virtually never the desired behaviour.

Another thing I do with almost every TextureRect is the following:

• Change expand_mode to ignore_size. This allows the TextureRect to be resized which is virtually always desired. If I wanted the TextureRect to always match the exact resolution of the texture I would probably want to do this explicitly.
• Change stretch_mode to keep_aspect_centered. This prevents the texture from being squeezed while ensuring it is fully visible, centered and contained within the bounds. This approach is not that common on the web but in my opinion it's usually the best approach.

These changes were not obvious to me when I first used Godot, and I think they would be helpful defaults to new users.

Summary of changes:

• Change default viewport size from 1152x648 to 640x360.
• Change default viewport stretch mode and aspect to canvas_items and expand.
• Change default TextureRect expand mode to ignore_size.
• Change default TextureRect stretch mode to keep_aspect_centered.

[Calinou]

Note that the first two project settings settings can't have their actual default value changed without breaking existing projects. This means new defaults should only impact newly created projects, using an approach similar to godotengine/godot#105737.

• Change default viewport size from 1152x648 to 640x360.

This is a sensible default for pixel art, but it's too low of a resolution for HD 2D art. It would also cause the default window size to be very small, although we could remedy this by specifying a default window size override. However, one problem with this is that we can't get integer scaling by using a default window size of 1280×720, as this resolution can't display properly in window mode on a 1366×768 display. Such displays are still present on some low-end laptops used by people in 2025, even though it's been years since no such laptops are being sold anymore.

This is the reason we went for 1152×648 as a default instead, as described in godotengine/godot#55032.

Project templates could be a better, more tailored solution to the problem.

• Change default viewport stretch mode and aspect to canvas_items and expand.

This was proposed in #3939, but we ended up deciding against it for a few reasons in 4.0. This could perhaps be revisited as I still think games should never use disabled, but there are still some considerations about it, especially when also using the expand stretch aspect.

• Change default TextureRect expand mode to ignore_size.
• Change default TextureRect stretch mode to keep_aspect_centered.

These two are not project settings but node properties, so we can't change their defaults without breaking existing projects.