1. Don't assume support for VK_KHR_get_memory_requirements2.
   Enable the extension, if supported, during device creation.
2. Also let VMA fill in the function pointers for these commands
   based on Vulkan API version -
   1. vkGetBufferMemoryRequirements2KHR
   2. vkGetImageMemoryRequirements2KHR

Bug: angleproject:4830
Change-Id: Icd0b3baf56732b5f5f49f320c1feb996204169ed
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2293633Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Mohan Maiya <m.maiya@samsung.com>