update useSelector() ts example in API Reference

[MayCXC]

The Hooks API Reference provides a simplified typescript definition for useSelector() that defines a type alias for SelectorFn, but then uses SelectorFunction in place of that type later in the example. This PR replaces the SelectorFunction usage with SelectorFn, and adds a generic type parameter to EqualityFn to resemble the definition of SelectorFn more closely, and updates the name of the equalityFn parameter to equalityFnOrOptions to match its current name in v8.

The example also puts an assignment statement const result: Selected = before a function declaration for useSelector, which is technically invalid typescript. Its meaning is clear, but it does not match how other hook API functions with parameters like createStoreHook, createDispatchHook, and createSelectorHook are introduced in the docs. With this in mind, it may be better to provide the type definition for useSelector in the example, and put the assignment statement in an inline comment instead:

type RootState = ReturnType<typeof store.getState>
type SelectorFn = <Selected>(state: RootState) => Selected
type EqualityFn = <Selected>(a: Selected, b: Selected) => boolean
export type DevModeCheckFrequency = 'never' | 'once' | 'always'

interface UseSelectorOptions {
  equalityFn?: EqualityFn
  devModeChecks?: {
    stabilityCheck?: DevModeCheckFrequency
    identityFunctionCheck?: DevModeCheckFrequency
  }
}

export const useSelector: <Selected>(
  selector: SelectorFn,
  equalityFnOrOptions?: EqualityFn | UseSelectorOptions
) => Selected

// Example usage:
// const result: Selected = useSelector(selector, equalityFnOrOptions)

Issue: #2152

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