[REQ][TypeScript Fetch] Default 3.6+ configuration to true

Is your feature request related to a problem? Please describe.

When I tried out the TypeScript fetch client generator, I got an error when viewing the generated code that GlobalFetch was not defined. GlobalFetch was removed in TypeScript 3.6.2. To fix this I had to change the configuration "typescriptThreePlus": true since it currently defaults to false. However the false default was set 2 years ago so it seems like a good time to revisit that.

Describe the solution you'd like

Update the typescriptThreePlus default to true since most users will be on something past TypeScript 3.6.2 at this point, and the defaults should work out of the box for most users.

Describe alternatives you've considered

There could just be extra documentation that clarifies the default, but that would likely be catering to a minority of new users at this point.

Additional context

Search the TypeScript fetch client generator for typescriptThreePlus and inspect where its default is defined. Change the default to true, then verify that generated output no longer references the removed GlobalFetch for TypeScript 3.6.2 and later.