Refactor AnyConst{16,32} types (#1552)

* use macros to generate Const16 impls

* use macro for Const32 from impls

* use macro to generate AnyConst16 from impls

* use u16 in AnyConst16

* use named bits field for AnyConst16

* use named bits field in AnyConst32

* apply rustfmt

* remove unnecessary comma

* move AnyConst16::from_bits up

* remove F{32,64} from impls from AnyConst32

* simplify AnyConst32 from impls

* generate from impls for AnyConst32 via macro

* swap method order

Author: Robbepop