docs: clarify onNavigate's full-page navigation behaviour

[nateeo]

given that beforeNavigate and afterNavigate are fired even on links with data-sveltekit-reload, initially I found it a bit confusing that onNavigate didn't, so it might be good to clarify that in some of the docs.

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[benmccann]

It seems odd to me that we'd mention it only on this one and not on the other lifecycle functions

Suggested change

	* A lifecycle function that runs the supplied `callback` immediately before we navigate to a new URL, except during full-page navigations.
	* A lifecycle function that runs the supplied `callback` immediately before we navigate to a new URL except during full-page navigations.

[nateeo]

before/afterNavigate mention that it occurs we navigate to a new URL, which I read as including full-page navigations. Happy to clarify it by mentioning that they run on full-page navigations?