Make `NavigationDuplicated` a no-op for `push` and `replace`

What problem does this feature solve?

Since a recent change every call to push or replace that is handed the same path as is currently active is rejecting with a NavigationDuplicated error and clients that don’t care about this duplication need to attach a no-op catch clause to all calls. I am aware that there was already a discussion on this topic in #2872 and can understand the viewpoints expressed by the maintainers there. However I’d still like to ask to reconsider this change and not reject for duplicated navigations.

The main arguments I would put into consideration against treating NavigationDuplicated as an error are:

• Not rejecting is more consistent with how <a> tags and <router-link> are working, i. e. I’d argue it is the API that is least surprising to users of vue-router because it is how browsers usually work.
• A client can already find out if a duplication is happening by looking at the current route and the push target if this functionality is desired. While this might be slightly more complicated for that use-case, the changed API puts a burden on all clients that don’t care about the duplication, which is IMHO the more common case.
• It essentially seems not possible anymore to call push without an attached catch because otherwise we might get irrelevant error logs, i. e. the API is now always (albeit minimally) more complex.
• Introducing the rejection was effectively a breaking change of the API for a lot of clients. The observable behaviour of pushing the same navigation twice was a no-op before and now it isn’t anymore.

What does the proposed API look like?

A duplicated navigation is a “no-op” or warning log in vue-router itself and doesn’t require clients to handle this in any way.

[dominik-bln]

So maybe this is a case that could benefit from configuration:

const router = new Router({
    routes: [],
    mode: 'history',
   // other options could be: 'reload', 'throw' and default to `throw` to avoid breaking changes
    duplicateNavigationPolicy: 'ignore'
})

[posva]

https://github.com/vuejs/rfcs/pull/150 addresses this 🙂