Fix Vulkan validation errors on default depth textures

[JFonS]

The validation layers were complaining that we use DEFAULT_RD_TEXTURE_WHITE (which is RGBA8) in places where it's sampled as a depth texture. This commit adds the new default texture DEFAULT_RD_TEXTURE_DEPTH and uses it where needed.

Here's the full validation error for reference:

Descriptor set VkDescriptorSet Descriptor Set 35356 encountered the following validation error at vkCmdDrawIndexed time: Descriptor in binding #4 index 0, VkImageView Image View 250, format VK_FORMAT_R8G8B8A8_UNORM, doesn't contain VK_FORMAT_FEATURE_2_SAMPLED_IMAGE_DEPTH_COMPARISON_BIT_KHR The Vulkan spec states: If a VkImageView is sampled with depth comparison, the image view's format features must contain VK_FORMAT_FEATURE_2_SAMPLED_IMAGE_DEPTH_COMPARISON_BIT (https://www.khronos.org/registry/vulkan/specs/1.3-extensions/html/vkspec.html#VUID-vkCmdDrawIndexed-None-06479)

[akien-mga]

Thanks!