Update examples to use `Image::new_target_texture` instead of manual image creation when possible (#23715)

# Objective

Fix #19101. (Kinda, this is not the exact solution proposed in that
issue, but it still shortens most of the examples)

## Solution

Most of the images created in examples are for use in render targets.
`Image::new_target_texture` is made for exactly that and significantly
shortens the image creation process.

## Testing

I tested all the examples I changed and they seem to work fine.

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btw for some reason most of the examples use
`TextureFormat::Bgra8UnormSrgb` while the documentation for
`Image::new_target_texture` recommends `TextureFormat::Rgba8UnormSrgb`
for SDR images. What's up with that?

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Co-authored-by: Carter Anderson <mcanders1@gmail.com>