hello_xr: add debug output for Vulkan extensions from runtime vs. app #214

Job	Run time
android / build-helloxr	2m 7s
android / loader	1m 10s
msvc-build / msvc-build (arm_uwp) / msvc-build	2m 56s
msvc-build / msvc-build (arm64_uwp) / msvc-build	3m 47s
msvc-build / msvc-build (win32) / msvc-build	4m 5s
msvc-build / msvc-build (x64) / msvc-build	3m 32s
msvc-build / msvc-build (win32_uwp) / msvc-build	3m 13s
msvc-build / msvc-build (x64_uwp) / msvc-build	3m 9s
msvc-build / organize-and-release-artifacts	0s
	23m 59s

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