Always include base `Sys` typedef && support typed `RichTextDataTarget`s

[anulman]

Summary

This PR extends the existing type definitions to support (1) full sys data; and (2) typed fields on RichTextDataTargets.

Description

N/A

Motivation and Context

I was trying to build my Typescript project, and it was throwing errors that were passing in dev (i.e. where typings weren't enforced).

Todos

N/A