Enforce stricter enum type checks

[kegsay]

When helping a colleague fix their usage of Go bindings, I was surprised that the types on enums were so weak as to be practically useless:

type SlidingSyncVersion interface {
	Destroy()
}
type SlidingSyncVersionNone struct {
}

func (e SlidingSyncVersionNone) Destroy() {
}

type SlidingSyncVersionProxy struct {
	Url string
}

func (e SlidingSyncVersionProxy) Destroy() {
	FfiDestroyerString{}.Destroy(e.Url)
}

type SlidingSyncVersionNative struct {
}

func (e SlidingSyncVersionNative) Destroy() {
}

Since the interface is just Destroy(), and most (all?) generated types have said function, it means there's no guidance into using the correct types. We could improve this if the bindings had a private named function e.g:

type SlidingSyncVersion interface {
	Destroy()
	slidingSyncVersion()
}
type SlidingSyncVersionNone struct {
}

func (e SlidingSyncVersionNone) slidingSyncVersion() {}

func (e SlidingSyncVersionNone) Destroy() {
}

type SlidingSyncVersionProxy struct {
	Url string
}

func (e SlidingSyncVersionProxy) slidingSyncVersion() {}

func (e SlidingSyncVersionProxy) Destroy() {
	FfiDestroyerString{}.Destroy(e.Url)
}

type SlidingSyncVersionNative struct {
}

func (e SlidingSyncVersionNative) slidingSyncVersion() {}

func (e SlidingSyncVersionNative) Destroy() {
}

Keeping it private avoids polluting the public API.