Samples should query existence and enable portability extension

[KarenGhavam-lunarG]

Due to the nature of VUID 04451, any existing app running on a portability platform (e.g., MoltenVK, gfx-rs) running validation will encounter new validation errors. To avoid the validation errors the application needs to query the existence of the extension and if present, enable the extension.

Might be nice to make the samples compliant by making these changes. But not high priority.

See this portability issue for more information.

For reference, VUID 04451 states:

If the VK_KHR_portability_subset extension is included in pProperties of
vkEnumerateDeviceExtensionProperties, ppEnabledExtensions must include
"VK_KHR_portability_subset".