Clean up depth format selection code

[SaschaWillems]

All samples that do depth buffering have code like this:

	void createDepthResources()
	{
		vk::Format depthFormat = findDepthFormat();

		createImage(swapChainExtent.width, swapChainExtent.height, depthFormat, vk::ImageTiling::eOptimal, vk::ImageUsageFlagBits::eDepthStencilAttachment, vk::MemoryPropertyFlagBits::eDeviceLocal, depthImage, depthImageMemory);
		depthImageView = createImageView(depthImage, depthFormat, vk::ImageAspectFlagBits::eDepth);
	}

	vk::Format findSupportedFormat(const std::vector<vk::Format> &candidates, vk::ImageTiling tiling, vk::FormatFeatureFlags features) const
	{
		for (const auto format : candidates)
		{
			vk::FormatProperties props = physicalDevice.getFormatProperties(format);

			if (tiling == vk::ImageTiling::eLinear && (props.linearTilingFeatures & features) == features)
			{
				return format;
			}
			if (tiling == vk::ImageTiling::eOptimal && (props.optimalTilingFeatures & features) == features)
			{
				return format;
			}
		}

		throw std::runtime_error("failed to find supported format!");
	}

	[[nodiscard]] vk::Format findDepthFormat() const
	{
		return findSupportedFormat(
		    {vk::Format::eD32Sfloat, vk::Format::eD32SfloatS8Uint, vk::Format::eD24UnormS8Uint},
		    vk::ImageTiling::eOptimal,
		    vk::FormatFeatureFlagBits::eDepthStencilAttachment);
	}

        ....
        // Somewhere in a function A
        vk::Format depthFormat = findDepthFormat();
        ....
        // Somewhere in a function B
        vk::Format depthFormat = findDepthFormat();

• findDepthFormat is often called multiple times of just querying once and then storing it.
• findSupportedFormat is only ever used in findDepthFormat
• findDepthFormat is declared after the calling function(s) createDepthResources

There is potential here to simplify code and make it easier to follow.