Emit d.ts files when mode is write-tsbuildinfo

[adriangodong]

This PR updates the write logic to also emit files ending with d.ts when mode is set to write-tsbuildinfo. This allows the plugin to work together with ts-loader or babel-loader and emits d.ts files without needing to run tsc.

[piotr-oles]

Why don't you use write-references instead?

[adriangodong]

Why don't you use write-references instead?

Wouldn't that mode overwrite the output of ts-loader?

[piotr-oles]

Ah, right. Could you add write-dts mode instead to keep it backward compatible?

[adriangodong]

Closing this in favor of a new mode, write-dts, implemented in #679