Description
There is a need to know what typescript versions are supported by the project since legacy typescript projects (Angular 8 etc.) use typescript versions that don't support the *.d.ts files generated in the latest 'lit' library (including 'lit-element', and, 'lit-html' libraries).
Typescript incompatibility described in lit/lit#2730 , lit/lit#2644 .
Steps to Reproduce, and Additional Details
See issues lit/lit#2730 , lit/lit#2644 .