Bug: incorrect TS function types

[taeh98]

• The types of the functions in index.d.ts are wrong
• None of them provide any types, and look like (...args: unknown[]): unknown;
• This is unhelpful since the types of arguments and return types aren't defined, so doesn't help enforce strict typing or tell library users which types to provide in arguments to functions or expect to return from them
• For example, onChange is defined as: onChange?(...args: unknown[]): unknown;
• onChange should be defined as: onChange?: (newValue: string | number | undefined) => void;