[TS] Improve autogen autocompletion and typing

[coolreader18]

Description of Changes

This changes the generated files for product type to be const Point = t.object(...); export default Point; instead of just export default t.object(...);, to match sum types. This lets intellisense know that it should be imported as import Point from ".../point_type.ts", not import point_type from ".../point_type.ts". It also adds a type Point = Infer<typeof Point>;, so that Point becomes both a type and a value, and users/we have to do less Infer<typeof Point>.

Expected complexity level and risk

1

Testing

n/a, no change in behavior.