types: assign type is note safe

[minx222]

when i use assign, i like

i's error.
i think it's type is safe.

declare const assign: <X extends Record<string | number | symbol, any>>(initial: X, override: X) => X;
like be

declare const assign: <X extends Record<string | number | symbol, any>, R extends Record<string | number | symbol, any> = T>(initial: X, override: R) => X & R;

[MarlonPassos-git]

@minx222 I would recommend you to take a look at Radashi(a fork of radash) where we fixed this problem.