wit/bindgen: Add JSON tag to Record structs

[lxfontes]

Related to #239

HostLayout receives json:"-" and any other field receives the original wit name.

// DateTime represents the record "wasi:clocks/[email protected]#datetime".
//
// A time and date in seconds plus nanoseconds.
//
//	record datetime {
//		seconds: u64,
//		nanoseconds: u32,
//	}
type DateTime struct {
	_           cm.HostLayout `json:"-"`
	Seconds     uint64        `json:"seconds"`
	Nanoseconds uint32        `json:"nanoseconds"`
}

[ydnar]

Don't forget to go generate ./tests/...

[ydnar]

How do we want to think about zero-value structs? Do we want to serialize, or have omitzero or omitempty?

[lxfontes]

Ideally I'd like omitzero, however by adding it we complicate:

• Tuples: encoded as lists. need to make sure we emit [ "field0", null, "field2"] and not ["field0","field2"]. Encoding it as dictionary would couple the json keys to cm.Tuple field names. I rather keep them as lists.
• Enums/Variants: The zero value is valid. I feel this is by WIT design so the first value acts as a sentinel, but it is up to developers to actually use it that way.

feels like omitempty would be the least problematic, not raising the issues above.

For now I'm adding omitempty and we can revisit if needed after addressing Variant encoding.

[ydnar]

Given that Go omits fields tagged with omitempty that are the zero value for the type, this may not be what we want.

Maybe we start without omitempty and then add it in certain cases as an optimization?

[lxfontes]

👍
removed omitempty.

[ydnar]

Looks ready to merge! Can you add a note to CHANGELOG.md?