Do not setup input buffers for function invocation as part of function registration

[pragnagopa]

Here is the flow from function load to invocation:

InputBuffer for function invocation on each function is created here:

azure-functions-host/src/WebJobs.Script/Description/Rpc/WorkerFunctionDescriptorProvider.cs

Lines 50 to 59 in 2b8c2b8

	protected override IFunctionInvoker CreateFunctionInvoker(string scriptFilePath, BindingMetadata triggerMetadata, FunctionMetadata functionMetadata, Collection<FunctionBinding> inputBindings, Collection<FunctionBinding> outputBindings)
	{
	var inputBuffer = new BufferBlock<ScriptInvocationContext>();
	_dispatcher.Register(new FunctionRegistrationContext
	{
	Metadata = functionMetadata,
	InputBuffer = inputBuffer
	});
	return new WorkerLanguageInvoker(Host, triggerMetadata, functionMetadata, _loggerFactory, inputBindings, outputBindings, inputBuffer);
	}

On Function Load response from a language worker, inputBuffer is linked to action block which is later used for invocation here:

azure-functions-host/src/WebJobs.Script/Rpc/LanguageWorkerChannel.cs

Lines 366 to 369 in 2b8c2b8

	var inputBuffer = _functionInputBuffers[loadResponse.FunctionId];
	// link the invocation inputs to the invoke call
	var invokeBlock = new ActionBlock<ScriptInvocationContext>(ctx => SendInvocationRequest(ctx));
	var disposableLink = inputBuffer.LinkTo(invokeBlock);

On function invocation, invocationContext is posted here:

azure-functions-host/src/WebJobs.Script/Description/Rpc/WorkerLanguageInvoker.cs

Line 73 in 2b8c2b8

_invocationBuffer.Post(invocationContext);

This triggers sending invocation request to language worker here:

azure-functions-host/src/WebJobs.Script/Rpc/LanguageWorkerChannel.cs

Line 373 in 2b8c2b8

internal void SendInvocationRequest(ScriptInvocationContext context)

If there is more than one language worker to handle an invocation, we need to be able to control where to post an invocation request. This would require setting up inputBuffers on each function load for every language worker that gets initialized.

Need to decouple setting up function invocation inputBuffers from WorkerFunctionDescriptorProvider.cs