Certain Vulkan extensions are marked as required despite being capabilities

[Mr-Wiseguy]

VK_EXT_ROBUSTNESS_2, VK_KHR_BUFFER_DEVICE_ADDRESS, and VK_KHR_SAMPLER_MIRROR_CLAMP_TO_EDGE are marked as required extensions, despite the first two being reported as capabilities and all three not being required for all consumers of plume:

plume/plume_vulkan.cpp

Lines 69 to 71 in df26845

	VK_EXT_ROBUSTNESS_2_EXTENSION_NAME,
	VK_KHR_BUFFER_DEVICE_ADDRESS_EXTENSION_NAME,
	VK_KHR_SAMPLER_MIRROR_CLAMP_TO_EDGE_EXTENSION_NAME,

These extensions are not required for RT64 and are not universally present, which would cause a regression when integrated that would prevent RT64 from running on machines that it can currently run on. VK_KHR_SAMPLER_MIRROR_CLAMP_TO_EDGE does not currently have an entry in the capabilities, so one should be added to report this to API consumers. Additionally, VK_EXT_SCALAR_BLOCK_LAYOUT is marked as a required extension but has a corresponding capability already as well. This was already marked as required in RT64 so it's not a regression there at least, but should probably not be required for consistency and because not all consumers will need it.