SL-84 and more improvements

[chris-miaskowski]

Summary

My changes rename *.ts to *.d.ts (explained why below). Karol's change improves the interface.

This is related to the build process and a typescript compilation error that is throw under the following conditions:

• a dependency (in this case this module) exports only .ts files
• an importer imports this dependency and has tsconfig/compilerOptions.composite: true
• this is either a TS bug or by design. I have identified the issue to be located here: https://github.com/Microsoft/TypeScript/blob/7ed9e44055d31949f2b633284f7bf8eed4abff96/src/compiler/program.ts#L2587
• i have reported that bug (added my finding to the conversation) here: TS6307 caused by ts files in excluded directory microsoft/TypeScript#27069

[billiegoose]

LGTM... IIRC ".d.ts" are "ambient declaration files". I don't know why it works that way, but I guess the idea is packages would normally export a CommonJS ".js" as main and then a "types-only" file as types.

[marbemac]

Looks good to me for now - I'm writing up a plan to finally organize our repos a bit better (hopefully :)).