Provide reasonable non-zero defaults for some structure fields

[jherico]

This would probably be something that would require some small amount of maintaining a customizer structure in the generation code, but there are a number of places where structures will be initialized to 0 when 1 would be a much better choice. The most apparent I can think of is within the SwapchainCreateInfo, where I can't think of a good reason not to default arraySize, sampleCount and faceCount to 1, since 0 is never a valid value for any of these.

I'm also tempted to suggest that the xr::ExtentXXX structures default to 1 or 1.0f, but I'm less certain if there's ever a legitimate use case for setting those values to 0.

[fredemmott]

Poses could also often default to { .orientation = {0, 0, 0, 1}, .position = {0, 0, 0} }, especially for ReferenceSpaceCreateInfo and ActionSpaceCreateInfo

[rpavlik]

I think we already have this? Quaternion is partially manually wrapped for this purpose.