Investigate TS 3.6, 3.7 support for TypeOfCoalesce<>

[AnyhowStep]

Something broke between 3.5 and 3.6. use git bisect and figure out what

microsoft/TypeScript#33541

[AnyhowStep]

Renaming because this issue was originally for a type that was breaking.

Another issue will be filed for general-purpose TS 3.6, 3.7 support