Add are_extension_features_present to PhysicalDevice

[n0F4x]

Implements #277

[charles-lunarg]

Oh, I thought individual feature checking was being asked for - not whether entire feature structs are present. Its much easier to check for structs and not features inside the struct.

I do like what I see here, it implements it cleanly.

[n0F4x]

This also makes it possible to check for individual features I hope.

The goal was to be able to write code like this:

VkPhysicalDeviceDescriptorIndexingFeatures descriptor_indexing_features{};
descriptor_indexing_features.<feature_to_be_checked> = true;

if (physical_device.are_extension_features_present(descriptor_indexing_features)) {
    // this individual <feature_to_be_checked> should be enabled
    // do something with this information
}

[charles-lunarg]

I hope you don't mind me going ahead and fixing a bug I found when I added some tests for the new function. Seemed like the best way to get it in, rather than have the normal 'back and forth' of requesting fixes and waiting for them to be implemented.

The feature was needed, so I appreciate you going ahead and adding it.