Added missing feature structure for VK_KHR_maintenance4
Added missing feature structure for VK_KHR_maintenance4

VK_KHR_maintenance4 adds a feature structure, which was missing from
PhysicalDevice::getFeatures2(). This CL adds it.

Tests: dEQP-VK.api.info.get_physical_device_properties2.features
Bug: b/204502926
Change-Id: I88738817a22e536c3b8c13887c5865f634cda403
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/64728
Presubmit-Ready: Alexis Hétu <1c7141772178a7e80858c3db5052b328076f08f4@google.com>
Reviewed-by: Nicolas Capens <51edc787c30f24c4904e8ffbb5523c3a9f7a451d@google.com>
Kokoro-Result: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Commit-Queue: Alexis Hétu <1c7141772178a7e80858c3db5052b328076f08f4@google.com>
Tested-by: Alexis Hétu <1c7141772178a7e80858c3db5052b328076f08f4@google.com>

google/swiftshader,google/swiftshader,google/swiftshader