Update specs for composite-type-value.initializers

[fxamacker]

Some changes to specs are required:

• Update composite-type-value.initializers from "one or many" to "zero or one" since only one initializer is supported and sorting is hard for multiple initializers.

• Remove deterministic sorting requirement for composite-type-value.initializers since only one initializer is supported and initializer parameters have natural sorting and shouldn't be changed.

Thanks @turbolent for great discussion and suggesting this today!