Specify `engines` property to package.json

[dahlia]

npm et al supports engines property in package.json, which indicates versions of supported runtime engines, e.g., Node.js v20+.

As we use dnt for generating package.json, we need to specify it in the dnt.ts script.

Our minimum requirements:

Runtime engine	Minimum version
Deno	1.41.0
Node.js	20.0.0
Bun	1.1.0