[0.8.x] Fallback pages

[timacdonald]

This PR is an alternative to #252 and #259.

It allows the path to be a string (current behaviour) or an array (new behaviour).

This enables two features:

1. A "fallback" so that users do not see a "whitescreen of death", where ./Pages/Whoops.vue is the fallback:

createInertiaApp({
    // ...
    resolve: (name) => resolvePageComponent([`./Pages/${name}.vue`, './Pages/Whoops.vue'], import.meta.glob('./Pages/**/*.vue')),
});

Of course, if the fallback isn't present things can still go wrong.

2. Easier migration from one file type to another without having to deal with error control, e.g., when migrating from .jsx to .tsx

createInertiaApp({
    // ...
    resolve: (name) => resolvePageComponent([`./Pages/${name}.tsx`, `./Pages/${name}.jsx`], import.meta.glob('./Pages/**/*.[tj]sx')),
});

[sh-sabbir]

@timacdonald Now that I see yours, it's indeed a better solution than mine