Arrayed specialization constants

[Firestar99]

Allows spec constants to be declared as arrays:

// single spec constants currently
#[spirv(spec_constant(id = 12, default = 34))] single: u32,
// spec constant arrays start at `id` and occupy consecutive ids, this uses id 42..46
// the default is the same for all values
#[spirv(spec_constant(id = 42, default = 69))] array: [u32; 4],

[LegNeato]

One small nit.

[LegNeato]

Suggested change

	"unsupported `#[spirv(spec_constant)]` type `{}` (expected `u32` pr `[u32; N]`)",
	"unsupported `#[spirv(spec_constant)]` type `{}` (expected `u32` or `[u32; N]`)",

[Firestar99]

oops, squashed