future-proof invalidate()

[Rich-Harris]

Closes #6354.

Related to #6489, #6274 and #5305 (we can remove the breaking change label from the latter two once this is merged).

It's very possible that we'd need to add an options object to invalidate(...) in future. Since overloaded functions are a terrible idea, that'd mean that to accommodate the no-argument case where you want to invalidate everything, we'd have to do this...

invalidate(undefined, {...});

...which is sinful. A better approach, which happens to be clearer and easier to document, is to create a new invalidateAll function:

<script>
-  import { invalidate } from '$app/navigation';
+  import { invalidateAll } from '$app/navigation';
</script>

-<button on:click={() => invalidate()}>reload</button>
+<button on:click={() => invalidateAll()}>reload</button>

Separately, I think it's probably more useful if the predicate form takes a URL instead of a string:

-invalidate((dep) => dep.includes('/some/matched/pathname'));
+invalidate((url) => url.pathname.startsWith('/some/matched/pathname'));

Unfortunately this second part is the sort of breaking change that's basically impossible to add a runtime error for. If people think a string (i.e. url.href) is preferable, then we could keep it as it is.

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