Mark all optional params correctly within JSDoc comments

[benjamincharity]

Currently our JSDoc comments do not explicitly mark optional params. We should add this for clarity.

• Mark all optional params by wrapping the param name in curly brackets:

// Existing
/**
 * Dispatches a keydown event from an element.
 *
 * @param type - The event type
 * @param key - The KeyCode type
 * @param target - The target element
 * @return The event
 *
 * @example
 * createKeyboardEvent('keydown', ENTER, myInputNativeElement);
 */

// After change:
/**
 * Dispatches a keydown event from an element.
 *
 * @param type - The event type
 * @param key - The KeyCode type
 * @param {target} - The target element
 * @return The event
 *
 * @example
 * createKeyboardEvent('keydown', ENTER, myInputNativeElement);
 */