Introduce `BunFile.append` or `Bun.append`

[TomasHubelbauer]

What is the problem this feature would solve?

With the introduction of BunFile.delete in Bun 1.2, the only remaining I/O method I have to tap to node:fs for is fs.promises.appendFile now. I think it would be really nice to be able to stick to Bun's native APIs for basic I/O.

What is the feature you are proposing to solve the problem?

I would like to propose one of the following:

• A new BunFile.append method
• A new Bun.append method with the same signature as Bun.write
• A new append boolean flag on Bun.write(destination, input, options)'s options

My preference would be the new BunFile.append method.

What alternatives have you considered?

Status quo, it's not so bad, my proposal is primarily motivated by desire for neatness.