Unify `NotFound` behavior across render modes

[ilonatommy]

Problems that we would like to solve:

• re-execution takes precedence over NotFound rendering,
• url of page is changed when we're streaming, having the blazor's router,
• not enough tests for each case, especially custom router tests.

This table presents current implementation for each combination of settings (Description) and actions to fix them (ToDo):

Application Interactivity	Content render mode	Default router	Description	ToDo
Global	SSR non-streaming	With	Renderer is setting the status code to 404 and stopping the rendering. Router tries to render 404 fragment but the component invoker decides to finish rendering early and not to flush the response because it expects re-execution. The only way to show 404 page is to re-execute, otherwise we would see a default browser’s not found page:	We should flush the response during rendering in component invoker regardless of returned code and re-execution middleware settings.
Per-component	SSR non-streaming	With	Same situation as global interactivity.	Row 1 solves it.
Global	SSR streaming	With	We use client side navigation that is same as typical client-based redirection but does not change the browser history if the request came with enhanced navigation switched on.	We could investigate different scenarios of 404 on POST request.
Per-component	SSR streaming	With	Same situation as global interactivity.	Row 3 solves it.
Global	Interactive	With	Same situation as 1st and 2nd scenario.	Row 1 solves it.
Per-component	Interactive	With	Impossible combination. We cannot render interactive page, not having interactivity registered for the application.	-
Any	SSR non-streaming	Without	The only way to render 404 page is to re-execute.	No action needed.
Any	SSR streaming	Without	Custom Router has to pass NotFoundPageRoute to NavigationManager.	Mechanism of passing the route is internal only, enable it publically.