Simplify unique extent check in RenderTarget<bindingType>::init functions

[asuessenbach]

Description

With #1517, we reduced the extent check in the RenderTarget<bindingType>::init functions from sorting the extents to counting the unique extents. But we actually just want to check if all extents are identical. And that can be easily done with this call to std::ranges::find_if. And this works regardless of whether VULKAN_HPP_HAS_SPACESHIP_OPERATOR is defined or not.

The previous approach nicely showed, how vulkan_hash.hpp can be used to use vulkan structs as the key in a std::unordered_set, but it's actually not needed.

Build tested on Win11 with VS2022. Run tested on Win11 with NVidia GPU.

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