Function xxx.say() should return message id, make Wechaty message easy to extend.

[su-chang]

Is your feature request related to a problem? Please describe.

When I want to recalled the message which I have send just now, I don't know the message unique id of it in Wechaty.

Describe the solution you'd like

The return type of function xxx.say() should change from Promise<void> to Promise<string>, let's make it return the message id for extend options.

For example:

public async contact.say(text: string): Promise<string>

const msgId = await contact.say('hello')
const messagePayload = await bot.Message.load(msgId)
// do something with the `messagePayload`

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.

[enhancement]

[huan]

I liked this idea. Would love to see your PR and study how you could implemented it.

After that, we will be able to discuss it in details.