Route lazy loading

The entire webpage defaults to loading all pages as soon as it is opened, and routing lazy loading means only loading the module you are currently clicking on.

Load the resources corresponding to the route on demand to improve the loading speed of the first screen (tip: the home page does not need to be lazy loaded, and a page will not be loaded again after it is loaded).

Implementation principle: The routing-related components are no longer imported directly, but are rewritten as asynchronous components, and the corresponding component content is loaded only when the function is called.