[Blazor] Adds support for server side rendered forms (without a body)

[javiercn]

No description provided.

[javiercn]

This is to avoid allocations altogether if we are not interesting on tracking event handlers. We only track them at the time we want to dispatch an event.

We actually want to avoid tracking events altogether when we are not trying to dispatch an event. That limits/eliminates any chance we introduce breaking changes if for example, someone have today multiple forms defined on their app without giving them unique event handler names.

[javiercn]

We need a new overload to track quiesce when we are dispatching an event to a named event handler. Alternatively, we can make quiescence a feature the renderer offers, and in that way, we don't have to be adding it to every API.

[SteveSandersonMS]

It's surprising to me that we need to return any quiescence-related Task from here. I would have expected that when Endpoints dispatches the event, that simply extends the existing QuiescenceTask that it was going to wait for anyway.

Perhaps that doesn't work out for some reason that is hard to understand. It would be great to clean this up but I would certainly understand if you don't want to block this PR on it. So I suggest:

• If you know clearly why it's not right for the existing QuiescenceTask to be extended by this dispatch, and don't think we should change it to do that, could you say why?
• Or if you think it would be reasonable for the existing QuiescenceTask to be extended by this dispatch, could you file an issue saying we should do that? I'd be happy to dig into what's going on and find out if I can do that.

[javiercn]

@SteveSandersonMS Everything is triggered from

aspnetcore/src/Components/Components/src/RenderTree/Renderer.cs

Lines 229 to 238 in 8968058

	protected internal async Task RenderRootComponentAsync(int componentId, ParameterView initialParameters)
	{
	Dispatcher.AssertAccess();
	// Since this is a "render root" operation being invoked from outside the system, we start tracking
	// any async tasks from this point until we reach quiescence. This allows external code such as prerendering
	// to know when the renderer has some finished output. We don't track async tasks at other times
	// because nobody would be waiting for quiescence at other times.
	// Having a nonnull value for _pendingTasks is what signals that we should be capturing the async tasks.
	_pendingTasks ??= new();

But when we wait for quiescence, we reset it after we are done (note the finally block):

aspnetcore/src/Components/Components/src/RenderTree/Renderer.cs

Lines 293 to 312 in 8968058

	private async Task WaitForQuiescence()
	{
	// If there's already a loop waiting for quiescence, just join it
	if (_ongoingQuiescenceTask is not null)
	{
	await _ongoingQuiescenceTask;
	return;
	}
	try
	{
	_ongoingQuiescenceTask = ProcessAsynchronousWork();
	await _ongoingQuiescenceTask;
	}
	finally
	{
	Debug.Assert(_pendingTasks is null || _pendingTasks.Count == 0);
	_pendingTasks = null;
	_ongoingQuiescenceTask = null;
	}

[SteveSandersonMS]

What's the difference between Name and BindingContextId? Developers might struggle to understand this as they sound like the same thing (also: the XML docs are duplicated).

Is there possibly any other name that could differentiate these more clearly?

[javiercn]

I've done a last round of cleanups and pushed and update. I might add a couple more streaming rendering tests, but otherwise, it should be good to go % feedback.

[MackinnonBuck]

LGTM, just some small questions/suggestions.