vk_bitflags_wrapped! should support const better

[thorjelly]

is_empty, intersects, and contains should all be const fn. Additionally, it would be very nice if there were intersection, union, difference const fn methods because bitwise operators do not work in const contexts except on stock integers. This is similar to how bitflags works: https://docs.rs/bitflags/1.3.2/bitflags/example_generated/struct.Flags.html

This would allow static validation directly on the bitflag types, as I am starting to do, to be a lot more convenient since they wouldn't need to be converted to/from raw to do any operations on them in a const context.